Field of the Invention

The invention relates to a decorative element, and in particular to a decorative element comprising a faceted body with a flat back surface and a concavo-convex microstructure provided on the flat back surface of the faceted body. Articles comprising the decorative element and methods of making the decorative element are also provided.

Background

Faceted decorative components such as gemstones and crystals have been used to embellish products for a long time. Conventional gemstones are usually grinded and polished by means of grinding wheels or rollers to obtain a convex outer shape comprising multiple sets of facets. The optical properties of gemstones are particularly important characteristics in this context, and these properties are defined at least in part by the geometry of the gemstone. The optical properties of a gemstone are often compared to those of a gemstone with a brilliant cut. The brilliant cut is a complex geometry with four different types of crown facets (including a table) and two different types of pavilion facets, all of which interact to create advantageous optical properties such as brilliance.

While the optical properties of traditional gemstones such as the brilliant cut are highly desirable, there are many disadvantages associated with these, primarily due to the fact that the geometries required to obtain these properties have a height (crown + pavilion) in the order of magnitude of the diameter of the gemstone. In particular, such voluminous gemstones cannot easily be glued on materials such as textiles or other flat surfaces, and holders are typically necessary to fix the gemstone in an upright position and mediate the contact with the substrate. Therefore, in such circumstances, gemstones without a pavilion (also referred to as ‘flat backs’) are typically used. Such components can be combined with a mirrored surface on the flat back in order to create a ‘sparkling effect’ where light incident on the mirror surface is reflected in multiple directions due to the interaction with the crown facets of the component. However, such flat backed gemstones typically have inferior optical properties compared to e.g. a brilliant cut, due to the absence of pavilion facets, even in the presence of a reflective layer.

It is against this background that the invention has been devised. Summary of the Invention

In a first aspect the invention provides a decorative element comprising: a faceted decorative body with a flat back surface, a microstructure on the flat back surface of the decorative body, wherein the microstructure comprises a faceted region, and an at least partially reflective layer on at least a portion of the faceted region of the microstructure; wherein the combination of the faceted region and the at least partially reflective layer is configured to reflect light incident on the at least partially reflective layer through the decorative body and/or the microstructure.

Suitably, the microstructure is configured to reflect light in multiple directions back through the microstructure and/or the decorative body. For example, light is reflected in a manner similar to that of a decorative body comprising a faceted pavilion rather than a flat back. Advantageously, the microstructure reflects light that passes through the decorative body at angles dictated by the refractive index of the microstructure and the angles of the faceted region, giving the appearance of a multifaceted decorative body, such as a decorative body comprising a pavilion having pavilion facets.

According to the invention, a faceted decorative body having a ‘flat back’ requires that the back side of the decorative body has at least a region that is substantially flat and aligned parallel to a girdle plane and/or table of the decorative body. Typically, a flat back implies that at least about 25%, at least about 33%, at least about 50%, at least about 66%, at least about 75%, at least about 80%, or at least about 85% of the surface area of the backside of the decorative body is flat and contiguous (and arranged parallel with the girdle plane / table of the decorative body). In some preferred embodiments the flat back of the decorative body comprises at least about 90%, at least about 95%, at least about 98%, at least about 99% or about 100% of the surface area of the back side of the gemstone. Generally, the flat portion of the decorative body is arranged centrally with respect to the back surface of the decorative body.

Suitably, the microstructure has a height of less than about 1,000 pm, less than about 500 pm, less than about 300 pm, less than about 200 pm; and/or at least about 10 pm, at least about 20 pm, at least about 30 pm, at least about 40 pm or at least about 50 pm or at least about 100 pm. The faceted region may be created by concave faceted portions of the microstructure. Suitably, the concave faceted portions of the microstructure have a depth of between about 1 pm and about 1,000 pm, between about 5 pm and about 500 pm, between about 10 pm and about 400 pm, between about 20 pm and about 300 pm, between about 30 pm and about 200 pm, or between about 40 pm and about 100 pm.

The combination of the depth and the angle of the facets relative to the flat-back surface determine the size, appearance and light reflecting effect of the faceted portion of the microstructure. Beneficially the facets are visible to the naked eye of the observer.

Advantageously, therefore, the facets in the faceted region are each inclined relative to the flat back surface of the faceted decorative body by an angle between about 1° and about 30°, between about 2° and about 25°, between about 3° and about 20°, or between about 4° and about 16°. In some embodiments, each of the facets is inclined relative to the flat back surface of the faceted decorative body by substantially the same angle as the other facets of the microstructure. In some embodiments, the angles between the facets in the faceted region and the flat back surface of the faceted decorative body are selected from one of two different angles. In some embodiments the facets are selected from one of three or one of four different angles. Where facets at more than one angle are used, the number of facets at each different angle is suitably the same. Preferably, the facets are arranged symmetrically on the microstructure.

In some embodiments, the facets of the microstructure may advantageously be defined by forming one or more pyramid profile within the microstructure, wherein each of the sides of the pyramid defines a facet of the faceted region of the microstructure. Thus, the sides of the pyramid are suitably planar. In such embodiments, the sides of the pyramid may be angled relative to the plane of the surface on which the microstructure is provided by an angle defined above. In some preferred embodiments, the facets defined by the pyramid are arranged at angles of between 5° and about 12°, such as about 6°, 7°, 8°, 9°, 10 or 11°. Typically, each facet of a pyramid is arranged at the same angle relative to the plane of the surface on which the microstructure is provided. A particularly preferred pyramid structure as facet angles of between about 10° and about 12°; for example, about 11°, such as about 11.2°.

Where the facets of the microstructure are defined by a pyramidal arrangement, the pyramid may have any appropriate number (x) of planar sides, for example, x may be an integer between 4 and 13; beneficially between 5 and 12; preferably between 6 and 11, such as 6, 7, 8, 9, 10 or 11. In some arrangements the facets / sides of the pyramid are equal size, e.g. for a 9-sided pyramid the sides are oriented at angles of 40° rotation relative to each adjacent side. However, in some embodiments, all sides / facets of the pyramid are not equally sized. For example, a pyramid may include two or three different sizes of facet. Preferably, the pyramid has rotational symmetry.

In some embodiments, the microstructure includes a single pyramid of facets. In such arrangements, the largest outer perimeter (i.e. the hypothetical base) of the pyramid may be substantially the same size as the surface of the microstructure. However, in some embodiments it may be preferable that the pyramid is smaller than the surface of the microstructure. In this regard, it may be convenient to consider the pyramid to have a radius (Pr), wherein the radius (Pr) defines a circle having a circumference that intersects the vertices of the base of the pyramid. In such embodiments, the radius defining the size of the pyramid may suitably be between about 20% and about 80% of the radius R of the largest circle that fits within the dimensions of the flat back. Preferably the pyramid has a radius (Pr) between about 30% and about 75% of the radius R, and more preferably between about 40% and about 66% of the radius R. For example, Pr may be about 60%, about 62%, about 64%, about 66%, about 68% or about 70% of the radius R. In one preferred embodiment the pyramid has 7 walls (facets), the angle of the facets is approximately 11° (e.g. 11.2°), and the pyramid has a radius Pr that is approximately 64% (e.g. 63.8%) of the radius of the flat back surface.

In embodiments wherein the facets of the pyramid do not cover the entire surface area of the microstructure on the planar back surface of the decorative body, the remainder of the microstructure may be planar, e.g. flat and on a plane parallel to the surface of the decorative body on which the microstructure is provided.

In other embodiments, the facets of the microstructure may advantageously be formed by a plurality of grooves, wherein the walls of the grooves create the facets in the microstructure. Suitably, the grooves comprise two planar walls that are angled relative to the flat back surface of the decorative body at angles of a and b, respectively. In such embodiments a and b may be the same for all of the grooves in the plurality of grooves. In some embodiments, a and b may be the same, whereas in other embodiments a and b may be different. Typically, the angle between each of the planar walls of the grooves and the flat back surface of the decorative body is individually selected from between about 1° and about 30°, between about 2° and about 25°, between about 3° and about 20°, or between about 4° and about 16°.

Conveniently, the grooves have a V-shape. However, in some embodiments the grooves may have a polygonal profile that is not strictly a V-shape. For example, each side wall of a groove may have two or more planar surfaces arranged at different angles relative to the flat base of the decorative body on which the microstructure is provided. Furthermore, in some embodiments, the base of the groove may be formed with a flat region rather than a sharp vertex.

Advantageously, the pattern of facets in the microstructure, or the pattern of grooves defining the facets in the microstructure may be symmetrical. The degree of symmetry of the facets / grooves of the microstructure may be the same or different to the degree of symmetry of the decorative body (where the decorative body has a defined symmetry). For example, in some beneficial embodiments, each grooves of the plurality of grooves is offset from each adjacent groove by an angle of rotation relative to a centre point or approximate centre point of the microstructure or decorative body (e.g. where the microstructure and/or the decorative body is not substantially circular). In embodiments, the grooves are rotated relative to each other by a constant angle about a(n approximate) centre point of the decorative body, and are located relative to each other to form an n-fold rotational symmetrical pattern. Thus, the angle of offset between each groove is selected to be 3607n.

In other embodiments, there may not be a constant offset / angle of rotation between adjacent grooves of the faceted portion of the microstructure. For example, there may be two to three different angles of rotation between adjacent grooves forming a single facet pattern within a microstructure. The angle of rotation between adjacent grooves may, for example, be selected from about 30°, about 40°, about 60°, about 90°, or any other appropriate angle. Desirably, the facet pattern has rotational symmetry. The degree of rotational symmetry, therefore, may not be equal to the number of grooves in the facet pattern.

In a preferred arrangement, the grooves are arranged on tangents to an imaginary circle centred on the flat back surface. Where the flat back is not circular, the centre of the flat back surface may be considered to be the centre of the largest circle that will fit within the dimensions of the flat back surface. The circle on which the tangents are determined for alignment of the grooves may have any appropriate radius (l_ _R ) between e.g. about 5% and about 95% of the radius (R) of the largest circle that defines / fits within the flat back surface. Beneficially, the circle has a radius (l_ _R ) that is between about 10% and about 90% of the radius R; more beneficially between about 20% and about 80% of the radius R; preferably between about 30% and about 75% of the radius R, and more preferably between about 40% and about 66% of the radius R. For example, l_ _R may be about 60%, about 62%, about 64%, about 66%, about 68% or about 70% of the radius R.

Thus, in any aspect or embodiment of the invention, the faceted region of the microstructure may comprise a pattern of facets that has n-fold rotational symmetry. Suitably n is an integer between 4 and 13; beneficially between 5 and 12; preferably between 6 and 11 , such as 6, 7, 8, 9, 10 or 11.

Similarly, the faceted decorative body according to any aspect or embodiment of the invention may have m-fold rotational symmetry. Suitably m is an integer between 4 and 13; beneficially between 5 and 12; preferably between 6 and 11, such as 6, 7, 8, 9, 10 or 11. In some embodiments n and m are the same. In some beneficial embodiments m is different to n. Optionally, the difference in value between n and m may be one integer: for example, n may be one higher than m (e.g. n may be 9 and m may be 8).

In some preferred embodiments, the decorative body is a flat back gemstone having a substantially circular girdle. In these and other embodiments, the faceted region of the microstructure beneficially is formed of 6, 7, 8 or 9 grooves equally spaced and oriented along tangents to an imaginary circle having a radius l_ _R of between 50% and 75% of the radius R of the largest circle that fits within the dimensions of the flat back surface. In one preferred embodiment, the facets of the faceted portion are defined by 6 linear grooves arranged respectively at 60° rotations about the imaginary circle relative to each adjacent groove, and at a radius l_ _R between about 64% and 66% of the radius R, or between about 87% and 89% of the radius R. In another preferred embodiment, the facets of the faceted portion are defined by 9 linear grooves oriented respectively at 40° rotations about the imaginary circle relative to each adjacent groove, and at a radius l_ _R between about 64% and 66% of the radius R, or between about 87% and 89% of the radius R. In these and other embodiments, the grooves within each faceted portion have the same cross-sectional profile; i.e. each groove is defined by a pairs of walls, wherein the walls are arranged at a defined angle with respect to the plane of the surface of the decorative body on which the microstructure is provided. Suitably, the angle of inclination of each of the walls is between about 4° and about 16°, more suitably between about 5° and about 10°, such as about 5°, about 6°, about 7° or about 8°. In some preferred embodiments, the angle of one wall of each groove (a) is different to the angle of the other wall of each groove (b). For example, the angle a may be about 4.9°, 5.3° or 5.4° and the angle b may be about 7.9°, 8.2° or 14.6°. In some preferred embodiments the wall of the groove having an angle a may be arranged towards the centre of the circle that defines the tangent on which the groove is aligned; whereas in some other preferred embodiments, the wall of the alignment of the grooves alternates such that a first groove is oriented such that the wall having an angle a is positioned towards the centre of the circle, and each adjacent groove is oriented such that the wall having an angle b is positioned towards the centre of the circle.

Typically, each of the plurality of grooves has two planar walls that are angled relative to the flat back surface of the decorative body at angles of a and b, respectively. In such embodiments a and b may be the same for all of the grooves in the plurality of grooves. In some embodiments, a and b may be the same, whereas in other embodiments a and b may be different.

In order to ensure effective light reflection without diffusion, it is important that the surfaces of the facets are flat and smooth. Beneficially, the facets are formed of planar surfaces with low surface roughness and a high degree of flatness. Suitably, the surface roughness is below about 100 nm, below about 50 nm, below about 20 nm, below about 10 nm, or below about 5 nm. Suitably, the flatness has a flatness deviation d _f below about 2 pm, below about 1 pm, below about 800 nm, below about 500 nm, below about 250 nm or below about 200 nm. Beneficially, the planar surfaces of the facets has a surface roughness that is below about 50 nm and a flatness deviation d _f below about 500 nm.

Conveniently, in some embodiments the microstructure may be formed integrally with the decorative body. In such embodiments, the microstructure may be formed by imprinting the flat back surface of the faceted decorative body. The imprinting is conveniently by imprint lithography, for example, nanoimprint lithography (NIL). In other embodiments in which the microstructure is formed integrally with the decorative body, the microstructure and decorative element may be formed as a single unit, for example, by sol-gel manufacturing processes, additive manufacturing / 3D printing, or injection molding. This can have the benefit of convenient manufacture and/or enabling the refractive index of the decorative body and microstructure to be exactly matched.

In some embodiments the microstructure is formed in a material applied to and formed on the decorative body after manufacture of the decorative body. Thus, the facets of the microstructure may be formed by imprinting a layer or material applied on the flat back surface of the faceted decorative body, such as by imprint lithography. In some embodiments the imprinting may be performed after the material of the microstructure has been applied to the decorative body, e.g. by nanoimprint lithography (NIL), while in some embodiments the facets may be imprinting on the microstructure before application to the decorative body (reverse NIL).

In some embodiments, the microstructure is made from a material obtained by curing a UV curable resin composition.

Suitably, the microstructure is formed of a material that has a refractive index that is similar to, such as within 30%, within 20%, within 10% or within 5% of that of the material of the decorative body. In this way, light travelling through and reflected by (internal) surfaces of the microstructure behaves similarly to light travelling through and reflected from the (internal) surfaces of the decorative body.

Preferably, the microstructure is formed of a transparent material. Similarly, the decorative body is preferably formed of a transparent material. Suitably, the faceted decorative body is a gemstone. The gemstone may be made of glass, crystal glass, glass ceramic, plastic or cubic zirconium.

The decorative body may be of any suitable size and shape; for example, the decorative body may be circular, oval, rectangular or square. In some embodiments the decorative body may be multi-sided and approximating towards a circle, oval, rectangle or square. The lateral dimensions of a decorative body according to the invention may range from between about 1 mm and about 250 mm. For example, between about 1 mm and about 150 mm, between about 2 mm and about 120 mm, between about 2 mm and about 100 mm, between about 3 mm and about 80 mm or between about 3 mm and about 60 mm, When the decorative body is circular, the decorative body may beneficially have a diameter in the above ranges. When the decorative body is not substantially circular, the term ‘diameter’ may refer to the diameter of the largest circle that would fit within the geometry of the decorative body. In some embodiments the height of the decorative body may be approximately the same as the diameter of the gemstone; for example, within 25%, within 20%, within 15% or within 10% of the diameter of the gemstone. Typically, the decorative body has a height between about 1 mm and about 120 mm, between about 1 mm and about 100 mm, between about 2 mm and about 80 mm, or between about 2 mm and about 60 mm.

The decorative element of any preceding claim, further comprising one or more protective layers on the at least partially reflective layer; and/or optionally further comprising an adhesive layer on the protective layer.

In a second aspect the invention provides a decorative element comprising: a decorative body comprising a front surface and a flat back surface, a microstructure on the flat back surface of the decorative body, wherein the microstructure comprises a faceted region, and an at least partially reflective layer on at least a portion of the faceted region of the microstructure; wherein the combination of the faceted region and the at least partially reflective layer is configured to reflect light incident on the at least partially reflective layer through the decorative body and/or the microstructure. For example, the decorative body may be a sheet material, such as a glass or plastics (polymeric) sheet material (e.g. a window or partition, such as a room divider or door). In other embodiments the front surface may be rounded (e.g. convex), but not faceted. For example, the decorative body may be a cabochon shape. Preferably, the decorative body is transparent.

Any one or combination or all of the features of the first or any other aspect of the invention, as described throughout this document, are explicitly intended to be applied to the second aspect of the invention and are not reiterated here purely for brevity.

In a third aspect the invention provides a decorative element comprising: a decorative body comprising a front surface and a back surface, a microstructure on the back surface of the decorative body, wherein the microstructure comprises a faceted region, and an at least partially reflective layer on at least a portion of the faceted region of the microstructure; wherein the combination of the faceted region and the at least partially reflective layer is configured to reflect light incident on the at least partially reflective layer through the decorative body and/or the microstructure. The front surface of the decorative body is beneficially a faceted surface, such as present in a gemstone. According to this aspect of the invention, the back surface of the decorative body on which the microstructure is provided is planar, i.e. it defines a contiguous flat or level surface arranged at a constant relative gradient. In accordance with this aspect, the back surface may be the surface of a ‘flat back’ decorative body / gemstone as defined in the first aspect of the invention. However, in other embodiments, the back surface of the decorative body on which the microstructure is provided may be an inclined surface or ‘facet’ located on the opposite side of the decorative body to the front surface (e.g. the planar back surface may be a pavilion facet). Where the decorative body has a girdle plane, the back surface may be inclined relative to (i.e. not parallel with) the girdle plane. Any angle of inclination may be selected according to the shape and structure of the decorative body. For example, the angle of inclination may be between about 1° and about 80°, between about 2° and about 70°, between about 3° and about 60°, between about 4° and about 50° degrees. Beneficially, the angle of inclination may be between about 5° and about 45°, between about 10° and about 40°, or between about 20° and about 30°. In other embodiments, the angle of inclination of the planar back surface may be measured relative to a ‘table’ of the decorative body. Where the decorative body does not have a classic ‘table’, e.g. because the decorative body is not a gemstone, then the ‘table’ may be considered to represent the largest planar surface on the front surface of the decorative body, and/or the girdle may be considered to represent the line / region around the decorative body at which the decorative body has its largest transverse cross-sectional area.

In this aspect, and any other aspect of the invention described herein, the facets of the faceted region of the microstructure suitably have a maximum facet dimension that is at least about 5 times smaller than a maximum dimension of the surface on which the microstructure is provided. Advantageously, the maximum facet dimension is at least about 10 times, at least about 15 times, at least about 20 times, at least about 25 times, at least about 50 times, or at least about 100 times smaller than a maximum dimension of the surface on which the microstructure is provided. In some embodiments, the facets of the microstructure have a surface area that is at least about 10 times, at least about 25 times, at least about 50 times, at least about 100 times, at least about 250 times, or at least about 500 times smaller than the surface area of the surface on which the microstructure is provided. In this way, advantageously, the faceted portion of the microstructure is able to increase the proportion and/or distribution of light that is reflected from the respective back surface of the decorative body in comparison to the decorative body in the absence of the microstructure. However, the facets of the microstructure are beneficially not so small that the reflected light to overly dispersed / fragmented. Preferably, the facets are a size that creates facet reflections that are visible with the naked eye of the observer.

Any one or combination or all of the features of the first or any other aspect of the invention, as described throughout this document, are explicitly intended to be applied to the third aspect of the invention and are not reiterated here purely for brevity.

In a fourth aspect of the invention, there is provided a method of making a decorative element, the method comprising: providing a faceted decorative body having a flat back surface; forming a microstructure on the flat back surface of the decorative body, wherein the microstructure comprises a faceted region; forming an at least partially reflective layer on at least a part of the faceted region of the microstructure, wherein the combination of the faceted region of the microstructure and the at least partially reflective layer is configured to reflect light incident on the at least partially reflective layer through the decorative body and/or the microstructure.

In a fifth aspect of the invention, there is provided a method of making a decorative element, the method comprising: providing a decorative body having a flat back surface; forming a microstructure on the flat back surface of the decorative body, wherein the microstructure comprises a faceted region; forming an at least partially reflective layer on at least a part of the faceted region of the microstructure, wherein the combination of the faceted region of the microstructure and the at least partially reflective layer is configured to reflect light incident on the at least partially reflective layer through the decorative body and/or the microstructure. According to embodiments of the invention the decorative body may be a sheet material, such as a glass or plastics (polymeric) sheet material (e.g. a window or partition, such as a room divider or door). In other embodiments the front surface may be rounded (e.g. convex), but not faceted. For example, the decorative body may be a cabochon shape.

In a sixth aspect of the invention, there is provided a method of making a decorative element, the method comprising: providing a decorative body comprising a front surface and a back surface; forming a microstructure on the back surface of the decorative body, wherein the microstructure comprises a faceted region; forming an at least partially reflective layer on at least a part of the faceted region of the microstructure, wherein the combination of the faceted region of the microstructure and the at least partially reflective layer is configured to reflect light incident on the at least partially reflective layer through the decorative body and/or the microstructure.

Suitably, according to any of the fourth, fifth and sixth aspects of the invention the microstructure is configured to reflect light in multiple directions back through the microstructure and/or the decorative body.

In some embodiments the steps of providing a decorative body comprising a front surface and a back surface and forming a microstructure on the back surface of the decorative body, wherein the microstructure comprises a faceted region comprises forming the microstructure and faceted region integrally with the decorative body, for example using a sol-gel manufacturing process, by additive manufacturing (e.g. 3D- printing) or by injection molding.

In some embodiments, the step of forming a microstructure comprises applying a layer of imprintable material onto the back surface of the decorative body and imprinting a microstructure into the layer of imprintable material using a stamp. Suitably, the imprintable material is curable composition, for example, a thermal, chemical or photo- curable composition, and the method comprises curing the imprintable material after or simultaneously with imprinting the composition. Conveniently, the material of the microstructure is a photocurable composition; preferably a UV-curable composition.

In some embodiments, the method of the fourth, fifth and/or sixth aspects of the invention may further comprise providing a working stamp for use in the method by replicating a master stamp into a polymeric stamp material. The master stamp may be a metallic master stamp, a hard metal master stamp or a non-metallic master stamp.

Advantageously, the master stamp and/or the working stamp has a low surface roughness and/or a high flatness. Beneficially, the flatness and roughness parameters match those specified in relation to other aspects and embodiments of the invention described herein.

Providing a metallic or non-metallic master stamp, suitably comprises creating a plurality of facets in a metal or microcrystalline substrate. Conveniently, the plurality of facets may be cut using a monocrystalline diamond cutting tool. The cutting profile of the cutting tool is suitably selected according to the desired facet pattern. For example, the monocrystalline diamond cutting tool may have a non-symmetrical triangular cutting profile. In such embodiments, creating a plurality of facets in the metal or non-metallic substrate may comprise creating a plurality of grooves with a monocrystalline diamond cutting tool, wherein the grooves have a V-shape corresponding to the shape of the monocrystalline diamond cutting tool. In other embodiments, the grooves may have a polygonal profile that is not strictly a V-shape. For example, the side walls of the groove may have two or more planar surfaces arranged at different angles relative to the flat base of the decorative body on which the microstructure is provided. Furthermore, in some embodiments, the base of the groove may have a flat region rather than a sharp vertex.

Conveniently, a single monocrystalline diamond cutting tool profile may be used to create all of the grooves of the microstructure, such that all of the grooves of a microstructure have a consistent profile.

In other embodiments, creating a plurality of facets in a metal or non-metallic substrate comprises creating a plurality of facets defining a pyramid in the substrate. In this way, the faceted region formed in the microstructure comprises a plurality of facets defining a pyramid shaped profile. Preferably, the pyramid in the microstructure is a concave pyramid in which the apex points towards the decorative element.

Advantageously, the methods of the invention are suitable for mass production of decorative elements, e.g. in a production line. Thus, the step of imprinting a microstructure into the layer of imprintable material using a stamp may suitably comprise providing a plurality of stamps on a support; and the step of providing a faceted decorative body may suitably comprise providing a plurality of decorative bodies on a carrier. Beneficially the support and/or carrier comprises an elastomeric material. An elastomeric material may compensate for manufacturing tolerances and/or allow the production process to be accurate and effective when the decorative bodies have slightly different sizes and/or are mounted at slightly different heights relative to the carrier.

Furthermore, in embodiments, providing a faceted decorative body may comprise providing a plurality of faceted decorative bodies and positioning the decorative bodies on a carrier by sieving the decorative bodies. The methods of the invention may further comprise transferring the sieved decorative bodies onto a centring plate, and then transferring the decorative bodies onto the carrier. Aspects and embodiments of the fourth, fifth and sixth aspects of the invention may comprise any or all of the features of the first, second and third aspects. In particular, any of the features of the decorative body, microstructure and any coatings or layers applied thereon and described in relation to the first, second and third aspects apply equally to the decorative body, microstructure and any coatings or layers applied thereon of the fourth, fifth and sixth aspects.

According to a seventh aspect, the invention provides an article comprising a decorative element according to any aspect or embodiment of the invention. In embodiments of this aspect, the article is a decorative article. Embodiments of this aspect may comprise a decorative element having any of the features of the decorative element of the first to sixth aspects.

For the avoidance of any doubt, embodiments of any of the aspects of the invention may comprise any of the features described in relation to any other aspect of the invention, unless such features are clearly not compatible. Furthermore, it is explicitly stated that any of the features of any embodiment of the invention are (where not obviously incompatible), intended and envisaged to be combined in any and all combinations; and all such combinations are hereby encompassed. Thus, by way of example, any one or more optional feature of the decorative body are intended to be combined with any one or more optional features of the microstructure and any one or more optional features resulting from the methods described; and any such resulting decorative element is considered to represent a decorative element according to the invention.

Brief Description of the Drawings

One or more embodiments of the invention will now be described, by way of example only, with reference to the appended drawings, in which:

Figures 1A, 1B and 1C show schematic top (Figure 1A), bottom (Figure 1B) and side (Figure 1C) views of a brilliant cut gemstone according to the prior art;

Figures 2 illustrates a framework to quantify the brilliance of a gemstone, exemplified using a brilliant cut as shown on Figures 1A to 1C, showing the pattern of light reflections towards the eye of a user looking at the gemstone from the top (table), originating from light in steep angle areas (22’), intermediate angle areas (24’), shallow angle areas (26’) relative to the plane of the girdle of the gemstone, and total / combined light reflection (28);

Figures 3A and 3B show the pattern of light reflection from the gemstone of Figures 1A to 1C (Figure 3A) and the brightness values along the section indicated by an inclined line on Figure 3A (Figure 3B);

Figures 4A, 4B, 4C and 4D show schematic cross-sectional views of decorative elements according to various embodiments of the invention;

Figures 5A, 5B and 5C show schematically the geometric configuration of facets in microstructures according to embodiments of the invention;

Figure 6A shows schematically the geometry of triangular grooves that may be used according to embodiments of the invention; Figure 6B shows schematically alternative geometries of grooves that may be used according to embodiments of the invention; Figure 6C shows schematically a configuration of sets of grooves that can be used according to embodiments of the invention to create a continuous pattern of facets; Figure 6D shows a perspective view of an example of a microstructure with a particular pattern of facets that can be created using the configuration shown on Figure 6C; and Figure 6E shows the same view of the microstructure of Figure 6D, but each of the nine panels is shaded to show the facets that are created by the side walls of one of each of the nine grooves shown on Figure 6D;

Figure 7 is a flowchart illustrating a method of making a decorative element according to embodiments of the invention, using nanoimprint lithography;

Figures 8A, 8B, 8C and 8D show schematic front side perspective views of circular flat back gemstones according to the prior art, with a ‘simple’ cut (Figure 8A, A2000 cut), an ‘advanced’ cut (Figure 8B, A2078 cut), a further ‘simple’ cut (Figure 8C, A2034 cut), and a further ‘advanced’ cut (Figure 8D, A2038 cut); Figures 8E and 8F show schematic front side perspective and side views, respectively, of a faceted flat back gemstone having a substantially square profile; Figure 9 shows the quantified fire value (relative to the maximum fire possible) and light return value (relative to the light return of Spectralon®) for the cuts of Figure 8A (A2000), Figure 8B (A2078), Figure 8C (A2034) and Figure 8D (A2038);

Figures 10A, 10B, 10C and 10D show the pattern of light reflections associated with the gemstone of Figure 8A: Figure 10A shows the pattern of light reflections (light grey) from shallow angle light; Figure 10B shows the pattern of light reflections (light grey) from intermediate angle light; Figure 10C shows the pattern of light reflections (light grey) from steep angle light; and Figure 10D shows the combined light reflections (light grey, dark grey) from shallow, intermediate and steep angle light;

Figures 11 A, 11 B, 11C and 11D show the pattern of light reflections associated with the gemstone of Figure 8B; Figure 11A shows the pattern of light reflections (light grey) from shallow angle light; Figure 11 B shows the pattern of light reflections (light grey) from intermediate angle light; Figure 11C shows the pattern of light reflections (light grey) from steep angle light; and Figure 11 D shows the combined light reflections (light grey, dark grey) from shallow, intermediate and steep angle light;

Figures 12A, 12B, 12C and 12D show the pattern of light reflections associated with the gemstone of Figure 8C: Figure 12A shows the pattern of light reflections (light grey) from shallow angle light; Figure 12B shows the pattern of light reflections (light grey) from intermediate angle light; Figure 12C shows the pattern of light reflections (light grey) from steep angle light; and Figure 12D shows the combined light reflections (light grey, dark grey) from shallow, intermediate and steep angle light;

Figures 13A and 13B show a microstructure according to embodiments of the invention; Figure 13A shows a perspective view of a microstructure suitable to be combined with a gemstone such as that of Figure 8A; Figure 13B is a diagram that shows the pattern of grooves that was used to create the geometry shown on Figure 13A; Figure 14 shows a decorative element according to the invention, combining the microstructure shown on Figure 13A and the gemstone shown on Figure 8A;

Figures 15A, 15B, 15C and 15D show the pattern of light reflections associated with the decorative element of Figure 14; Figure 15B shows the pattern of light reflections (light grey) from shallow angle light, Figure 15C shows the pattern of light reflections (light grey) from intermediate angle light, Figure 15D shows the pattern of light reflections (light grey) from steep angle light, and Figure 15A shows the combined light reflections (light grey, dark grey) from shallow, intermediate and steep angle light;

Figures 16A and 16B show a microstructure according to embodiments of the invention; Figure 16A shows a perspective view of a microstructure suitable to be combined with a gemstone such as that of Figure 8C; Figure 16B is a diagram that shows the pattern of grooves that was used to create the geometry shown on Figure 16A;

Figure 17 shows a decorative element according to the invention, combining the microstructure shown on Figure 16A and the gemstone shown on Figure 8C;

Figures 18A, 18B, 18C and 18D show the pattern of light reflections associated with the decorative element of Figure 17; Figure 18B shows the pattern of light reflections (light grey) from shallow angle light, Figure 18C shows the pattern of light reflections (light grey) from intermediate angle light, Figure 18D shows the pattern of light reflections (light grey) from steep angle light, and Figure 18A shows the combined light reflections (light grey, dark grey) from shallow, intermediate and steep angle light;

Figures 19A and 19B show a microstructure according to embodiments of the invention; Figure 19A shows a perspective view of a microstructure suitable to be combined with a gemstone of Figure 8B; Figure 19B is a diagram that shows the pattern of grooves that was used to create the geometry shown on Figure 19A;

Figure 20 shows a decorative element according to the invention, combining the microstructure shown on Figure 19A and the gemstone shown on Figure 8C; Figures 21 A, 21 B, 21 C and 21 D show the pattern of light reflections associated with the decorative element of Figure 20; Figure 21 B shows the pattern of light reflections (light grey) from shallow angle light, Figure 21 C shows the pattern of light reflections (light grey) from intermediate angle light, Figure 21 D shows the pattern of light reflections (light grey) from steep angle light, and Figure 21A shows the combined light reflections (light grey, dark grey) from shallow, intermediate and steep angle light;

Figures 22A, 22B and 22C show a microstructure according to embodiments of the invention in plan view (Figure 22k), and perspective views of stamp elements (Figures 22B, 22C) that can be used to create a pyramidal facet pattern such as that of Figure 22A;

Figure 23 shows a decorative element according to the invention, combining the microstructure shown on Figure 22k and the gemstone shown on Figure 8B; and

Figures 24A, 24B, 24C and 24D show the pattern of light reflections associated with the decorative element of Figure 23; Figure 24B shows the pattern of light reflections (light grey) from shallow angle light, Figure 24C shows the pattern of light reflections (light grey) from intermediate angle light, Figure 24D shows the pattern of light reflections (light grey) from steep angle light, and Figure 24A shows the combined light reflections (light grey, dark grey) from shallow, intermediate and steep angle light.

Detailed Description

The inventors have surprisingly discovered that a decorative element with superior optical properties could be obtained by combining a faceted decorative body with a flat back surface (i.e. a flat back gemstone or crystal) with a concavo-convex microstructure on the flat back surface of the decorative body.

By ‘concavo-convex’ it means that the microstructure contains parts which point inwards, i.e. which are concave.

Throughout this description, the terms ‘back’ / ‘bottom’, and ‘front’ / ‘top’ surface are used to refer to the surfaces of a decorative element / faceted transparent body / gemstone that when incorporated in an article (such as e.g. when applied to the surface of an article), are intended to face towards a viewer (front / top surface), or away from a viewer, such as towards the surface on which the decorative element / faceted transparent body / gemstone is applied or supported (back / bottom surface), respectively. However, the skilled person will appreciate that decorative elements / faceted transparent bodies / gemstones may have a complex geometry, as required by the circumstances, and as such a back or front surface may, in fact, comprise a collection of jointed or disjointed surfaces. In practice, a front surface is intended to be visible in use, whereas a back surface is intended to be attached to or otherwise combined with an article.

Figures 1A, 1B and 1C show schematic top (Figure 1A), bottom (Figure 1 B) and side (Figure 1C) views of a brilliant cut gemstone 1 as known in the art. The gemstone 1 comprises a crown 2, a pavilion 6, and a girdle 4. The crown 2 forms the top (or ‘front’) part of the gemstone 1. In the case of a brilliant cut as illustrated on Figures 1A to 1C, the crown comprises a large flat facet 12 called the ‘table’ which is parallel to the plane of the girdle 4, and three types of crown facets 8, 10, 14 provided between the table 12 and the girdle 4. Facets 8 are commonly referred to as ‘bezel facets’. Facets 10 are commonly referred to as ‘star facets’. Facets 14 are commonly referred to as ‘upper half facets’. The gemstone illustrated on Figures 1A to 1C has an eight-fold symmetry in both the crown 2 and the pavilion 6. As such, the crown comprises an octagonal table 12, eight star facets 10, eight bezel facets 8, and sixteen upper half facets 14. Pairs of upper half facets 14 alternate with single bezel facets 8 around the upper perimeter of the girdle 4. The pavilion 6 forms the bottom (or ‘back’ or ‘lower’) part of the gemstone 1. In the case of a brilliant cut as illustrated in Figures 1A to 1C, the pavilion 6 comprises two types of facets. A first set of pavilion facets 16 is commonly referred to as ‘pavilion main facets’ and meet at an apex 20. The apex 20 may be an apex in the strict geometric sense of the word, or may be in the form of a small flat facet referred to as a ‘culet’. The culet, when present, is typically significantly smaller than the other pavilion facets. A second set of pavilion facets 18 is commonly referred to as ‘lower half facets’. As the gemstone illustrated on Figures 1A to 1C has an eight-fold symmetry in the pavilion 6, the pavilion 6 comprises eight pavilion main facets 16 and sixteen lower half facets 18. Pairs of lower half facets 18 alternate with single pavilion main facets 16 around the lower perimeter of the girdle 4.

The girdle 4 is the region that forms the junction between the crown 2, and the pavilion 6, if present. As such, the girdle 4 is the region at which the gemstone has its largest transverse dimension. The girdle is associated with an imaginary plane P _G , referred to as the ‘plane of the girdle’ or ‘girdle plane’, illustrated by the dashed line on Figure 1C. The plane P _G is arranged such that all of the crown facets (and all of the pavilion facets, if present) within a set of facets have essentially the same orientation and distance to the plane P _G , when taking into account symmetries in the set. For example, the upper half facets 14 are provided in pairs where each pair comprises facets that mirror each other. Within the context of the invention, a ‘set’ or ‘type’ of facets refers to a group of facets that are substantially identical in shape, and that have the same or symmetrical orientations relative to the girdle plane P _G . Further, the plane P _G is arranged such that it is parallel to the table 12.

In order to characterise the optical properties of a gemstone, a series of parameters which collectively define the ‘brilliance’ of a gemstone have been defined by the Gemological Institute of America in Moses et ai, 2004 (Gems & Gemology, Fall 2004, Vol. 40, No. 3, https://www.gia.edu/gems-gemology/fall-2004-grading-cut-qual itv-brilliant- diamond-moses). These parameters are now standard in the art and include the fire, light return and scintillation. The fire of a gemstone refers to the extent of light dispersed into spectral colours seen in a polished gemstone when viewed face-up. The light return is the extent of internal and external reflections of ‘white’ light seen in a polished gemstone when viewed face-up. The scintillation is the appearance of spots of light seen in a polished gemstone when viewed face-up that flash as the gemstone, observer, or light source moves (also referred to as ‘sparkle’) and the relative size, arrangement, and contrast of bright and dark areas seen in a polished gemstone when viewed face-up while that gemstone is still or moving (also referred to as ‘pattern’). Scintillation can be quantified using an apparatus and set up defined by the American Gemological Society in J. Sasian et ai (Evaluation of brilliance, fire, and scintillation in round brilliant gemstones, Optical Engineering, 46(9), 093604 (2007)) and P. Yantzer et ai (Foundation, Research Results and Application of the New AGS Cut Grading System, https://cdn.vmaws.eom/www.americangemsociety.org/resource/re smgr/docs/AGSLab/A GS-Cut-Svstem.pdf), as shown in Figure 2 which exemplifies the set up for a brilliant cut as shown on Figures 1A to C.

The system for measuring parameters of a gemstone as illustrated in Figure 2 comprises using a light source around a hemisphere H centred on the gemstone 1 and extending from the girdle plane P _G of the gemstone 1 under evaluation, and evaluating the influence of light coming from different angles along the hemisphere H on light reflections seen by an observer O looking at the gemstone from the front / top (i.e. perpendicular to the girdle plane P _G , through the table 12 of the gemstone if present). The hemisphere H is divided into three distinct segments 22, 24, 26, and the light reflections caused by illumination of these segments are separately evaluated. The hemisphere H is divided into a segment 26 of shallow-angle light, a segment 24 of intermediate angle light, and a segment of steep angle light 22. The pattern of reflections shown caused by light in each of these segments can be represented as separate shallow-angle, intermediate-angle and steep-angle representations 26’, 24’, 22’, respectively; and these can be combined into a single representation 28. Analysis of such patterns have indicated that an ideal brilliant cut as shown in Figures 1A to 1C should have about 15% of steep-angle light areas (shown as dark areas in the pattern 22’, relative to the complete surface area of the reflection pattern), which are evenly distributed and preferably display a star-like pattern; and where the steep-angle light areas do not comprise a large compact light area in the centre (i.e. no dark area in the centre of pattern 22’). An ideal brilliant cut should also preferably have a high fraction of intermediate-angle light areas (shown as dark areas in the pattern 24’), and a small fraction of shallow-angle light areas (shown as dark areas in the pattern 26’). A gemstone with such properties, such as e.g. the brilliant cut of Figures 1A to 1C can have light return and fire values of about 69% and 50%, respectively, for light return and fire, for an Ideal Cut (Tolkowsky) diamond, where light return and fire may be measured according to the Gemological Institute of America (GIA) standard as set out in Moses et al. , 2004 (Gems & Gemology, Fall 2004, Vol. 40, No. 3, https://www.gia.edu/gems-gemology/fall-2004-grading-cut-qual ity-brilliant-diamond- moses), as implemented in WO 2015/027252 A1, which is incorporated herein by reference. In particular, fire can be quantified as a percentage of the maximum possible fire (all white light incident on the gemstone is reflected onto a measurement area and the colour saturation of this reflected light is complete), and the light return can be quantified as a percentage compared to the light return that would be obtained from a sample of Spectralon® of the same size as the gemstone under evaluation.

Figure 3A shows the pattern of light reflection from the gemstone of Figures 1 A to 1C under spot illuminance, as imaged on a screen placed 50 cm away from the stone. Figure 3B shows the brightness values (y-axis represents brightness (arbitrary units), x- axis represents consecutive pixel number) along the section indicated by an inclined line on Figure 3A. Data such as that shown on Figure 3A enables to visualise the fire of a specific cut, whereas data such as that shown on Figure 3B shows the contrast between light and dark areas generated by reflection spots, which represents the sparkle of the specific cut.

As previously mentioned, gemstones such as the one shown on Figures 1A to 1C may not be practical in all circumstances, despite their beneficial optical properties, due to their bulky geometry. As further discussed in Example 1 below, flat back gemstones, which do not comprise a pavilion 6 and have a substantially flat back surface do not have the same problems as regards mounting to a flat surface, for example, as traditionally cut gemstones, but have substantially worse optical properties. Against this background, the inventors have discovered that it is possible to obtain a decorative element that combines the advantages of traditional cut gemstones in terms of optical properties, and the advantages of flat back gemstones in terms of ease of application and versatility.

Figures 4A, 4B, 4C and 4D show schematic cross-sectional views of decorative elements 400, 400’, 400”, 400’” according to embodiments of the invention. The decorative elements 400, 400’, 400”, 400”’ comprise a faceted body 100 (also referred herein as ‘gemstone’) which comprises a crown 120, a girdle 140, and a flat back surface 150. The crown 120 comprises one or more sets of main crown facets 110 and a flat table 130. The table 130 and the flat back surface 150 are substantially parallel. In the embodiments shown, the girdle has a height H _G and the crown has a height H _c (as indicated on Figure 4A), leading to a total gemstone height H _G s = H _G +H _C . The gemstone may, in accordance with the invention, have any suitable size; for example, gemstone heights of up to 250 mm are envisaged. In embodiments, the total height of the gemstone may be between about 1 mm and about 150 mm, between about 1 mm and about 100 mm, between about 1 mm and about 80 mm, between about 1 mm and about 50 mm, or between about 1 mm and about 25 mm. Suitably, the gemstones may have a total height of about 1 mm to about 20 mm, from about 2 mm to about 15 mm or between 3 mm and about 10 mm. The height H _G of the girdle is typically significantly smaller than the height H _c of the crown, such as e.g. about 10% of the height H _c of the crown. However, as the skilled person would understand, the particular geometry of the gemstone is not limited and in particular the gemstone may have any number of crown facets, may have any number of sets of crown facets, may lack a flat table, and/or may have a girdle 140 that has a height of approx. 0 mm, such that the crown facets extend to the flat back. Further, the size of the gemstone is also not limited in theory, although it would typically be in the order of millimetres or centimetres. Figures 8A to 8D show perspective views of examples of gemstones that can be used for the purpose of the invention.

The decorative elements 400, 400’, 400”, 400’” comprise a concavo-convex microstructure 200 provided on the flat back surface 150 of the gemstone 100. The microstructure has a first major surface 210 and a second major surface 220. In the embodiments shown, the microstructure 200 is provided directly in contact with the flat back surface 150 of the gemstone 100, such that the first major surface 210 is in contact with the flat back surface 150 of the gemstone. In some such embodiments, the gemstone 100 and the microstructure 200 may be integrally formed such that surfaces 150 and 210 are virtual / internal. In some embodiments, one or more layers of material may be provided between the microstructure 200 and the flat back surface 150 of the gemstone 100. For example, a primer layer may be provided between the microstructure 200 and the flat back surface 150 of the gemstone 100. This may advantageously increase adhesion between the microstructure 200 and the flat back surface 150, depending on the material(s) forming the gemstone 100 and the microstructure 200. The microstructure 200 has a height H _M which is the highest distance between the first major surface 210 and the second major surface 220 (and is not necessarily shown in scale with respect to the gemstone 100 in Figures 4A to 4D). The second major surface comprises a plurality of facets 230. Within the context of the invention, facets are substantially planar surfaces of any geometry that are adjacent to each other and meet at sharp edges or vertices, in a similar manner as the cut sides of a gemstone. In the embodiments shown on Figures 4A, 4C and 4D, the facets 230 form a continuous pattern of facets 230 that extends over the entire second major surface 220 of the microstructure 200. In other embodiments, such as that shown on Figure 4B, the second major surface 220 comprises a faceted region 220A and a substantially flat region 220B. In the embodiment shown in Figure 4B, the faceted region 220A is surrounded by a continuous flat region 220B, and the faceted region 220A is a concave pyramid shape. As the skilled person would understand, other configurations are possible. However, configurations including a faceted region in the centre of the second major surface and located over the centre of the flat back surface 150 are believed to be particularly advantageous as they may beneficially provide facets directly underneath a region of the gemstone that is typically flat, the table 130. Further, each of the faceted region 220A and flat region 220B may be continuous or may comprise a plurality of disjointed faceted / flat regions. The height H _M of the microstructure 200 is advantageously below 1,000 pm, preferably below about 500 p , typically below about 300 pm, beneficially below about 200 pm and preferably below about 100 pm. The height H _M of the microstructure 200 is preferably at least about 1 pm, at least about 5 pm, at least about 10 pm, at least about 20 pm, at least about 30 pm or at least about 40 pm. Microstructure facet heights within these ranges may maintain the benefits of a flat back gemstone, e.g. in relation to ease of handling and application, and may also enable the creation of patterns of facets that are large enough to be visible with the naked eye, such that the microstructure is able to create patterns of light reflection that are similar to those of gemstones. Further, heights within these ranges may be advantageously achieved with techniques such as nanoimprint lithography, as will be described further below. The depths of the concave portions of the microstructure are advantageously of a similar order of magnitude as the height H _M of the microstructure. For example, the depths of the concave portions of the microstructures may advantageously be between about 1 pm and 1 ,000 pm or between about 5 pm and about 500 pm; suitably between about 10 pm and about 300 pm or between about 20 pm and about 200 pm, and preferably between about 30 pm and about 100 pm.

The decorative elements 400, 400’, 400”, 400’”, according to these embodiments, further comprise an at least partially reflective layer 240. The combination of the facets 230 and the at least partially reflective layer ensures that light that is incident on the reflective layer 240 through the gemstone and microstructure is reflected towards the front of the decorative elements. Further, the facets are configured such that the light is reflected in multiple directions back through the gemstone, thereby enhancing the gem-like appearance of the decorative element. For example, parallel light rays incident on the gemstone through the table 130 would be reflected on the layer 240 in at least two directions due to the inclination of the facets 230 on which the reflective layer 240 is applied. In the embodiments shown, the at least partially reflective layer 240 is provided directly in contact with the second major surface 220 of the microstructure 200. In embodiments, one or more additional layer(s) of material may be provided between the second major surface 220 of the microstructure 200 and the at least partially reflective layer 240, for example, in order to increase the adhesion between the microstructure 200 and the at least partially reflective layer 240, and/or to include an optical property modifying layer such as e.g. a coloured layer. In the embodiments shown, the at least partially reflective layer is provided on a surface that covers substantially the whole second major surface 220 of the major structure. In embodiments, the at least partially reflective layer is a reflective layer, also referred to herein as a mirror layer. In embodiments, the reflective layer is a metallisation layer. Any mirror coating known in the art may be suitable for use in the present invention. For example, mirror layers comprising a silver, aluminium or rhodium coating may be used. In embodiments, the at least partially reflective layer is a layer of metal, such as e.g. a silver, aluminium or rhodium layer, with a thickness of between about 20 nm and about 1 pm. Reflective layers such as metal coatings are known in the art. In embodiments, the at least partially reflective layer is provided on a region that covers most (such as e.g. 90%, 95%, 98%, or 99%) or all of the second major surface 220 of the microstructure 200.

In some embodiments, e.g. as shown on Figures 4C and 4D, the decorative elements 400”, 400’” further comprise a protective layer 250. In the embodiments shown, the protective layer 250 is applied directly on the reflective layer 240 and is provided on a surface that covers substantially the whole second major surface 220 of the microstructure. The protective layer 250 is advantageously provided over a surface that covers at least the surface on which a reflective layer 240 is provided. A protective layer 250 may advantageously protect the microstructure, or a reflective layer applied thereon, from damage, particularly before the decorative element is attached to a surface.

In embodiments, the protective layer comprises a layer of lacquer. Where used, the lacquer may be applied with a thickness of between about 3 and about 20 pm, such as between about 4 and about 14 pm (e.g. 9 ± 5 pm); for example, the lacquer may be applied with a thickness of about 9 pm. In some embodiments, the layer of lacquer comprises a lacquer selected from the group consisting of: epoxy lacquers, one component polyurethane lacquers, bi-component polyurethane lacquers, acrylic lacquers, UV-curable lacquers, and sol-gel coatings. The lacquer may additionally ensure that the decorative element according to the invention is bondable. As the skilled person would understand, the choice of a suitable lacquer may depend on the material to which the decorative element is intended to be bonded, and/or on the adhesive that is intended to be used. The lacquer may optionally be pigmented.

In embodiments, the lacquer may be applied by spraying, digital printing, rolling, curtain coating or other two-dimensional application methods known in the art, such as screen printing, pad printing, micro dispensing, flexoprinting, rotary screen printing, inkjet printing, roller application or reverse NIL. Suitably, the lacquer may be selected so as to be mechanically and chemically robust and bondable. In this regard, a lacquer may be considered to be mechanically and chemically robust if it would not substantially degrade or allow degradation of an underlying reflective layer in the conditions that would be expected in the intended use. For example, the decorative structure may advantageously show high resistance to any of sweat, machine washing, temperature changes, sun exposure, and suitable performance in anti-corrosion salt spray and climate tests. Resistance to machine washing may be tested by subjecting a sample of the decorative structure to 10 cycles of machine washing at 40°C, optionally followed by drying, and examining the decorative structure for any visible damage with the naked eye. Suitable performance in climate tests may be tested by exposing a sample of the decorative structure to climate tests (e.g. exposure to the environment or a simulated environment) for 480 hours, and examining the decorative structure for any visible damage with the naked eye. Resistance to sweat may be tested by putting a sample of the decorative structure in contact with artificial sweat for 48 hours, and examining the sample for any visible damage with the naked eye. Resistance to temperature changes may be tested by subjecting a sample of the decorative structure to 20 cycles of temperature changes, and examining the sample for any visible damage with the naked eye. For example, a cycle of temperature changes may comprise exposing the decorative element to a temperature of about 70°C, followed by a sudden transfer to -20°C, then to room temperature (such as e.g. between 20° and 25°C). Resistance to sun exposure may be tested by subjecting a sample of the decorative structure to a simulated solar energy of 13.8 MJ/m ² and examining the decorative element for any visible damage with the naked eye. For example, the sample may be subjected to light between about 300 and about 800 nm at about 650 W/m ² for a period of about 48 to 72 hours, such as about 62.8 hours. Suitable performance in anti-corrosion salt spray may be tested by exposing a sample of the decorative element to sea water tests for 96 hours, and examining the sample for any visible damage, with the naked eye.

In the embodiment shown on Figure 4D, the decorative element 400’” further comprise a layer of pre-applied adhesive 260. The use of pre-applied adhesive may enable easy application of the finished decorative element to the surface of an article. As the skilled person would understand, the features of the layer of pre-applied adhesive 260 and/or protective layer 250 may be combined with any geometries of the microstructure, including, in particular, geometries where the second major surface comprises a continuous pattern of facets that extends substantially over the whole area of the second major surface 220, and geometries where the second major surface 220 comprises a first faceted region 220A and a second, substantially flat region 220B. Suitably, the adhesive may be a non-reactive thermal adhesive, also known as hot-melt adhesive. Advantageously, a pre-applied hot-melt adhesive may enable easy application of the gemstone to many surfaces including e.g. garments and textiles, etc. In embodiments, the layer of adhesive may have a thickness between about 50 pm and about 400 pm, such as between about 100 pm and about 200 pm. Advantageously, layers of hot melt adhesive in the above ranges may provide for sufficient adhesion even on porous substrates such as textiles. When the layer of hot melt adhesive is too thick, the risk of the hot melt adhesive spilling out when the decorative element is applied to a surface increases, resulting in possible application problems, loss of aesthetic quality, and waste of adhesive. As the skilled person would understand, the optimal amount of hot-melt adhesive to be applied may depend on the particular geometry of the microstructure. In some embodiments, the hot melt glue is a copolyamide-based glue, such as Griltex® 1A from EMS-CHEMIE. In some embodiments, the hot melt glue is a thermoplastic polyurethane-based glue, such as VP 1006 by Collano® AG.

According to any embodiments of the invention, the refractive index of the material of the gemstone / faceted body may be at least about 1.45. Beneficially, the material of the gemstone has a refractive index of at least about 1.5 and not more than about 1.8, such as between about 1.55 and about 1.7. Physical properties such as the refractive index influence the path of the light through a gemstone. As such, refractive indices within these ranges may further increase the brilliance of the gemstone.

Suitably, the faceted body / gemstone is made of a transparent material. The term ‘transparent’ is used throughout this disclosure to refer to a material that has a transparency higher than zero. In the context of the present invention, a material is called transparent if it allows the transport of light, suitably at least visible light. Preferably, the material is transparent in the conventional sense, i.e. allowing (at least visible) light to pass through the material without being scattered.

The gemstone can be made of a wide variety of materials. For example, the gemstone may be made of glass, plastic or cubic zirconium. In some embodiments, the gemstone is made of crystal glass. Transparent bodies made of glass or plastic are preferred, because they are low cost, non-conductive and are most readily provided with facets. Gemstones made of glass, and in particular crystal glass (e.g. as defined by the European Crystal Directive (69/493/EEC)), are particularly preferred, for their superior optical properties.

The invention is not limited in principle with respect to the composition of the glass. ‘Glass’ in this context means any frozen supercooled liquid that forms an amorphous solid. Oxidic glasses, chalcogenide glasses, metallic glasses or non-metallic glasses can be employed. Oxynitride glasses may also be suitable. The glasses may be one- component (e.g. quartz glass) or two-component (e.g. alkali borate glass) or multi- component (e.g. soda lime glass) glasses. The glass can be prepared by melting, by sol- gel processes, by shock waves or by any other appropriate means. Such methods are known to the skilled person. Inorganic glasses, especially oxidic glasses, are preferred. These include silicate glasses, soda lime glasses, borate glasses or phosphate glasses. Lead-free crystal glasses are particularly preferred.

In embodiments, the gemstone is made of soda lime glass. Suitably, the faceted transparent body may alternatively be made of lead and barium-free crystal glass. Examples of suitable lead and barium-free crystal glass compositions for use in accordance with the present invention are disclosed in e.g. EP 1725502 and EP 265149, the contents of which are incorporated herein by reference.

As another raw material for the preparation of the gemstone, plastics can be employed. Transparent plastics are preferred. Among others, the following materials are suitable: acrylic glass (polymethyl methacrylates, PMMA); polycarbonate (PC); polyvinyl chloride (PVC); polystyrene (PS); polyphenylene ether (PPO); polyethylene (PE); poly-N- methylmethacrylimide (PMMI).

An advantage of using a plastics material over glass in the manufacture of transparent bodies for use in the present invention resides, in particular, in the lower specific weight, which may be only about half that of glass. In addition, other material properties may also be selectively adjusted. Further, plastics are often more readily processed as compared to glass. Some disadvantages of the use of plastics materials include the low modulus of elasticity and the low surface hardness as well as the massive drop in strength at temperatures from about 70°C and above, as compared to glass. A preferred plastic is poly-N-methylmethacrylimide, which is sold, for example, by Evonik under the name Pleximid ^® TT70. Pleximid ^® TT70 has a refractive index of 1.54, and a transmittance of 91% as measured according to ISO 13468-2 using D65 standard light.

In some embodiments, the gemstone is coloured. By way of example, the colouring may be provided as a colouring agent throughout the material of the gemstone. Alternatively, or in addition to colouring the body of the material, a colouring may be provided as a coating or surface treatment on at least a region of a surface of the gemstone. For example, a coating or surface treatment may be provided on at least a region of the crown facets and/or at least a region of a substantially flat back surface of the gemstone.

Colouring and decorative coatings may enable the gemstone to be provided with a variety of decorative effects, improving their flexibility of use. Such colourings and decorative coatings are preferably configured so that the gemstone remains transparent to light entering through the crown facets.

In embodiments, the largest transverse dimension of the gemstone (also referred to herein as its diameter) may be between about 1 and 250 mm, between 1 and about 150 mm or between 1 and about 100 mm. Beneficially, the transverse dimension may be between about 1 and 80 mm, between 1 and 60 mm, between 1 and 40 mm, between 1 and 20 mm, or between 2 and 12 mm. In some embodiments, the girdle may be substantially circular. In embodiments where the girdle is not substantially circular, the term ‘diameter’ may refer to the diameter of the smallest circle that would fit the geometry of the girdle.

In accordance with the invention, the microstructure 200 may be formed from a polymeric material, which is suitably obtained by curing a resin or lacquer. In other words, the microstructure 200 may be obtained by shaping and curing a curable resin or lacquer to obtain a solid microstructure. Beneficially, the microstructure is made from a transparent material. Advantageously, the use of a transparent material enables visible light to travel through the material of the microstructure such that it can be at least partially reflected by the at least partially reflective layer, where the combination of faceting and reflection results in an improvement in the optical properties of the decorative element compared to a flat back gemstone with a reflective layer. The microstructure may be formed or shaped by imprinting, such as by imprint lithography. Alternatively, the microstructure may be formed by moulding, such as e.g. injection moulding, thermoforming, or casting, directly on the gemstone, or integrally with the gemstone. Thus, in some embodiments the microstructure may be formed together with the gemstone, such that a combined structure comprising the crown of the gemstone and a microstructured back surface may be formed.

In embodiments, the microstructure may be made from any polymer that is suitable for imprinting, as known in the art. In some embodiments, the microstructure is made from hybrid polymers. For example, hybrid polymers commercialised under the name OrmoClear® from micro-resist technology GmbH may be suitable. In some embodiments, the microstructure is made from UV-curable or thermally curable resins / lacquers. In some embodiments, the microstructure may be made from a thermosetting material, such as e.g. sol-gel or polycarbonate. The microstructure may be made from a material obtained by curing a curable resin composition, for example, a UV curable resin composition. This may enable the microstructure to be provided by forming a resin composition in a plastic state then curing it to obtain a substantially solid structure.

The microstructure is beneficially made from a material that has a refractive index that is similar to that of the material of the gemstone / faceted body. For example, the microstructure may be made from a material that has a refractive index between about 1.4 and about 2.42, and beneficially between about 1.52 and about 2.18. In embodiments, the microstructure may be made by curing a resin / lacquer that, when cured, has a refractive index within the above ranges and, preferably, that is similar to that of the material of the gemstone / faceted body.

Preferably, the material of the microstructure is chosen to be compatible with the material of the gemstone / faceted body and/or with the material of the at least partially reflective layer. In particular, the materials may be considered to be compatible if they show good levels of adhesion and/or do not adversely react with each other. The skilled person is able to determine whether such materials are compatible using his / her common general knowledge and/or by routine experimentation.

In embodiments, the microstructure is made by curing a resin / lacquer that, in the uncured state, has a viscosity that is sufficient to remain on the surface on which it is applied during imprinting, but not so high as to be difficult to apply. In embodiments, the curable resin / lacquer composition has a viscosity below about 3.5 Pas or below about 3.3 Pas: for example, between about 0.5 and about 3.5 Pas, between about 1.0 and about 3.4 Pas, between about 1.5 and about 3.3 Pas; and suitably between about 2.0 and about 3.2, or between about 2.6 and about 3.2 Pas. A preferred composition has a viscosity of around 2.9 Pas. Advantageously, curable compositions with a pre-cured viscosity in the above ranges may be conveniently applied as thin uniform coating films. For example, a suitable resin composition may have a pre-cured viscosity such that the compositions can be applied in layers of the thickness described above in relation to layer 200; for example, between about 1 pm and about 300 pm. This may be particularly advantageous for use in nanoimprint lithography.

Preferably, the microstructure is made by curing a resin / lacquer that exhibits low shrinkage during curing. A resin / lacquer composition may be considered to have low shrinkage if the volumetric shrinkage during curing (i.e. difference in volume between the uncured composition and the cured composition) is below about 10%, below 7%, below 5% or below 2%.

As best shown on Figure 5A, the facets 230 of the microstructure 200 are each inclined relative to the plane of the flat back surface 150 of the gemstone by a characteristic angle a, b. In embodiments, all of the facets 230 of the microstructure are inclined by the same characteristic angle, or are adjacent to facets that are inclined by the same characteristic angle, as shown on Figure 5B. In embodiments, the microstructure comprise a first group of facets 230a inclined relative to the surface 150 by a first angle a, which are adjacent to a second group of facets 230b inclined relative to the surface 150 by a second angle b, where a and b are different, as shown on Figure 5C. Advantageously, facets 230 that are all inclined relative to the surface 150 by the same angle or by one of two angles a, b may be obtained by creating a plurality of triangular grooves 28, as best shown on Figures 6A and 6B, where each groove of the plurality of triangular grooves comprises a first planar wall 28a inclined with a first angle a relative to the surface 150, and a second planar wall 28b inclined with a second angle b, where a and b can be the same or different (as illustrated on Figures 6A and 6B), meeting at an apex 32. In the embodiments shown on Figure 6A, the microstructure comprises a plurality of grooves 28 that are substantially parallel and each comprise a first planar wall 28a inclined with a first angle a relative to the surface 150, and a second planar wall 28b inclined with a second angle b, where a and b are different. In the top embodiment shown on Figure 6A, the grooves 28 are arranged such that the first planar wall 28a of each groove is adjacent to the second planar wall 28b of the preceding groove (and conversely, the second planar wall 28b of each groove is adjacent to the first planar wall 28a of the subsequent groove, i.e. the first and second planar walls 28a, 28b alternate). In the bottom embodiment shown on Figure 6A, the grooves 28 are arranged such that the first planar wall 28a of each groove is adjacent to the first planar wall 28a of the preceding groove (and conversely, the second planar wall 28b of each groove is adjacent to the second planar wall 28b of the subsequent groove, i.e. the orientation of the first and second planar walls 28a, 28b alternate between subsequent grooves 28). The angles a, b between the facets / planar walls and the flat back surface 150 of the gemstone may advantageously be chosen to be between 2° and 25°. Indeed, such values may result on advantageous fire and scintillation when combined with conventional flat back gemstones. Additionally, lower angles may result in facets that are too large compared to the size of the gemstone and/or that do not generate a gem-like pattern of light reflections. On the other hand, steeper angles may result in facets that are too small to be visible with the naked eye, within the range of thickness of the microstructure that is amenable to nanoimprint lithography and similar techniques, and/or that do not generate a gem-like pattern of light reflections. The precise combination of angles that will result in the best gem-like appearance may depend on the geometry of the microstructure and the gemstone. As such, ray tracing softwares may be used to define optimal geometries, as exemplified below.

In the embodiment shown on Figure 6A (and in Figures 4A, 4C, 4D), the microstructure 200 comprises a plurality of grooves 28, 28’, which are ‘triangular’ profile grooves formed from two planar walls 28a, 28b, that meet at an apex 32. However, as best seen on Figure 6B, the grooves may comprise two planar walls 28a, 28b that meet at a flat base 28c. In such embodiments, the flat base 28c is preferably narrow. For example, the width of the planar base is less than the depth of the groove; less than 0.5x the depth of the groove; or less than 0.25x the depth of the groove. In embodiments, the grooves may comprise a lower portion G _L comprising two planar walls 28a’, 28b’ that in the embodiment shown meet at an apex 32’ (although in other embodiments these may alternatively meet at a flat base) and upper portion Gu comprising walls 28c’, 28d’, at least one of the walls 28c’, 28d’ extending at an angle from the walls of the lower portion such that one or both side walls comprises two angular planes / two facet angles (i.e. wherein the angle of the facet wall section relative to the plane of the gemstone base 150 is different for each wall section). In embodiments, the concept can be extended to grooves that have three or more planar portions (e.g. a lower portion, one or more middle portion(s) and an upper portion, where each portion comprises two walls, at least one of the walls extending from the corresponding wall of the preceding portion at an angle).

Figure 6C illustrates an arrangement of a plurality of grooves 28 that together create a continuous pattern of facets 230, such as that shown on Figure 6D. Figure 6C shows the shape of the second major surface 220 of the microstructure, which in this case matches the back surface 150 of the gemstone, where in this embodiment both are circular, and depicts the location of each of nine grooves 28. Each of the grooves 28 is perpendicular to a radius R of a circle C that is centred on the centre of the flat back surface 150 / second major surface 220, and that has a length l_ _R . In the illustrated embodiment, l_ _R is selected to be approximately 65% of the radius of the circle of the flat back surface 150 / second major surface 220. The grooves 28 form a symmetrical pattern with nine-fold symmetry, i.e. each groove is rotated by 40° around the central axis of the circle. Each of the grooves 28 comprises a first planar wall 28a and a first planar wall 28b, each creating facets 230 as previously described. The walls 28a, 28b of each of the grooves 28 may be inclined at the same angle a=b, or different angles a¹b, as explained above. Further, each groove 28 may have angles a, b that differ from one or more of the other grooves 28. Figure 6D shows a perspective view of an example of a microstructure with a particular pattern of facets 230 that can be created using the configuration shown on Figure 6C, with nine grooves rotated by 40°, each groove having a¹b, but where each a and each b are identical across all nine grooves and identically oriented (i.e. the first planar wall 28a with angle a is closer to the centre of the structure than the second planar wall 28b with angle b). Each of the grooves 28 is highlighted using a dashed line overlaid on the image. Figure 6E shows the same view of the microstructure of Figure 6D, but each of the nine panels is coloured to show the facets that are created by the walls 28a, 28b of one of each of the nine grooves 28. As can be seen on Figures 6D and 6E, the relatively simple pattern of grooves shown on Figure 6C can be used to generate a microstructure with a complex pattern of facets that has the ability to, when combined with an at least partially reflective layer, reflect light back through the gemstone in multiple directions in a gem-like manner. In particular, it is advantageous if the grooves are arranged to generate a pattern that has high light return, fire and scintillation as explained above, in a similar way to that of gemstone cuts.

The pattern of facets of the microstructure, like that of the gemstone on which it is applied, typically has rotational symmetry. For example, the pattern shown on Figure 6E has nine-fold rotational symmetry. By contrast, the flat back gemstone shown on Figure 8A has eight-fold rotational symmetry. Preferably, the geometry of the microstructure is designed such that rotational alignment of the microstructure and the gemstone is not necessary in order to obtain a gem like appearance. This may advantageously increase the simplicity of the production process. For example, a nine-fold symmetrical microstructure may be combined with an eight-fold symmetrical flat back gemstone. In this way, for example, it is not necessary to properly align the orientation of the gemstone with the orientation of the microstructure, thus simplifying the construction process.

Figure 7 is a flowchart illustrating a method of making a decorative element according to embodiments of the invention, using nanoimprint lithography.

At step 700, a master stamp for imprinting is provided. A master stamp is typically a metallic structure that can be used to replicate a pattern onto a working stamp. For example, a nickel or nickel phosphorus stamp may be used. The step of providing a metallic master stamp may comprise creating a plurality of facets in a metal substrate using a monocrystalline diamond cutting tool. In embodiments, the plurality of facets may be created by forming a plurality of grooves, as explained above. Alternatively, the plurality of facets may be created by forming a pyramid shape (or reverse groove) as shown on Figure 4B and Figure 22C, using a monocrystalline diamond cutting tool.

In some embodiments, a master stamp may be created as a single part, for example by cutting grooves to create a single pattern that corresponds to the entire surface of the microstructure. In other embodiments, a master stamp may be created as a plurality of parts, which may then be assembled, as best shown on Figures 22B and 22C. In other embodiments, a master stamp may be generated by grayscale lithography, 2-photon absorption or any other method known in the art. However, the use of a monocrystalline diamond cutting tool is thought to be preferable as it may result in a master stamp that has advantageous surface properties. Advantageously, the use of a monocrystalline diamond cutting tool may enable the creation of a metal master stamp that has very low surface roughness and high flatness, thereby ultimately resulting in a microstructure that itself has low surface roughness and high flatness and, as a result, better optical properties. Indeed, stray light that may be generated by high surface roughness may reduce the brilliance of the decorative element by creating a slightly white appearance of the facets and a reduction in the contrast between light and dark areas of the reflection pattern generated by the decorative element. Further, curved facets (i.e. low flatness) may spread reflected light in a broader angle range and lead to a reduction in the fire of the decorative element by mixing of coloured light rays which would not be mixed by reflection on a flat facet. Suitably, the master stamp has a surface roughness Ra below about 100 nm, below about 50 nm, below about 20 nm, below about 10 nm, or below about 5 nm. Advantageously, the master stamp has a flatness deviation d _f below about 2 pm, below about 1 pm, below about 800 nm, below about 500 nm or below about 200 nm. Preferably, the master stamp has a surface roughness below about 10 nm and a flatness deviation d _f below 500 nm. Master stamps with a surface roughness below about 5 nm and a flatness deviation d _f below 250 nm may be particularly advantageous.

The monocrystalline diamond cutting tool may be chosen to have a symmetrical triangular shape, to create grooves as shown on Figures 5A and 5B, or to have a non- symmetrical triangular shape, e.g. to create grooves as shown on Figure 5C. Advantageously, the use of a monocrystalline diamond cutting tool that has a non- symmetrical triangular shape may enable to create grooves that have walls at two different angles without having to rotate the diamond cutting tool relative to the metal substrate. The ability to create grooves with walls at different angles enables the creation of microstructures that have at least two different types of facets that differ by their angle relative to the plane of the support. Further, the ability to obtain this geometry without requiring rotation of the cutting tool relative to the master stamp reduces the complexity of the cutting machine that is used to produce the stamp. Further, the geometry of the microstructure could be increased in complexity by including flat facets (i.e. facets that are parallel to the flat back surface 150) in the pattern of facets. These can be achieved, for example, by cutting grooves in the material of the master stamp such that small areas of the master stamp remain untouched (i.e. such that the walls of the grooves do not all meet at a sharp angle, but instead are spaced apart by a flat region). In order to obtain the desired levels of surface roughness and flatness, these flat surfaces can be ground and polished, or cut with a diamond cutting tool with a 0° angle.

At step 710, one or more working stamp(s) are produced by replicating the metallic master stamp. Any polymeric stamp material suitable for use in nanoimprinting technologies may be used in the present invention. In particular, the working stamps may be made of PDMS (polydimethylsiloxane), or using a polyurethane-acrylate resin, for example, a UV curable polyurethane-acrylate resin. The working stamp preferably has low surface roughness and high flatness. For example, the working stamp may have a surface roughness Ra below about 100 nm, preferably below about 50 nm, below about 20 nm, below about 10 nm, or below about 5 nm. Beneficially, the working stamp has a flatness deviation d _f below about 2 pm, preferably below about 1 pm, below about 800 nm, below about 500 nm or below about 200 nm.

The one or more working stamps are typically provided on a support, such as, for example, an imprinting roller. In embodiments, the working stamps may be fixed directly on a solid support (e.g. a metallic roller) or may be separated from the solid support by one or more flexible layers. Advantageously, the use of flexible layers between the wording stamp and solid support may help to increase the tolerance of the process to sight difference in distances between the working stamp and the material to be imprinted (for example due to slight differences in the height of the gemstones on which the microstructure is provided). Suitable materials for use as the one or more flexible layers are known to the skilled person. For example, a soft PVC material may be used. A soft PVC layer may have a thickness of approx. 2 to 3.5 mm, for example, about 2.7 mm. Subsequent process parameters can be adapted to the hardness of the flexible layers, as would be known to the person of skill in the art.

At step 720, one or more faceted bodies (gemstones) are provided. The gemstones may be produced using any process known in the art, and may include, in particular, a cutting step 720a, a polishing step 720b and a cleaning step 720c as known in the art. Alternatively, ready-made faceted bodies / gemstones may be sourced for the purpose of the invention.

At step 730, the gemstones are positioned on a carrier. Advantageously, the gemstones are located precisely on the carrier according to a predetermined positioning. Precise positioning of the decorative bodies on a carrier is beneficial, particularly when the working stamps that will be used for imprinting are provided at fixed positions on a support, as is generally convenient. As such, the respective positions of the working stamps and gemstones can be aligned for accurate imprinting. Positioning of the gemstones on a carrier may include the step of sieving 730a a plurality of gemstones to roughly locate each gemstone at a known point on a grid (wherein rotational alignment between the stamp and the gemstone may not be required). The sieved gemstones may then optionally be centred 730b by transferring the gemstones from a sieving plate to a centricity plate. A centricity plate may for example comprise a plurality of rubber rings in which the gemstones are centred in the x-y direction. Transfer to a centricity plate may further increase the positional accuracy compared to sieving alone. Preferably, the gemstones are positioned with a precision (tolerance) below about 0.1 mm. Finally, the gemstones are then fixed onto a carrier. For example, this may be achieved by transferring the gemstones from the sieving plate / centricity plate to a vacuum plate and then applying on the gemstones a plate of thermoplastic material in a plastic state such that the gemstones are at least partially embedded in the carrier. The thermoplastic material may then be cooled to a relatively solid state. In other embodiments, the carrier may comprise an adhesive tape that is applied onto the gemstone. Alternatively, a vacuum plate may be used as a carrier. In yet other embodiments, the gemstones may be deep drawn in a plastic layer, such as polypropylene or polycarbonate.

In embodiments, the carrier is made from or comprises an elastic material, such as e.g. a rubber-like material. Some elasticity in the carrier may advantageously help to compensate for differences in the level (height) of the surface to be imprinted, between the gemstones on the carrier. Preferably, the carrier is made from or coated with a material that has chemical resistance to the chemicals used in the production process (including e.g. any coatings, cleaning agents, etc.) and to the process parameters used during production (e.g. temperature, humidity etc.). Further, the carrier is preferably made from or comprises a material that enables the fixation of the gemstones in the x, y and z directions (using an adhesive or by embedding the gemstones in the material, as explained above). Additionally, the carrier material preferably has good adhesion with the gemstones, such that additional adhesive (which would have to be separately applied and removed, thereby increasing process complexity) is not required. Preferably, the carrier material does not exhibit significant dimensional changes when exposed to the temperatures used in the process. For example, when the carrier material is a thermoplastic material, the material preferably has low shrinkage during cooling. Finally, it is advantageous for the carrier material to enable residue-free release of the gemstones / decorative bodies after imprinting. In embodiments, a thermoplastic material such as Gutta-percha (a rubber-like elastomer) may advantageously be used.

The gemstones are beneficially located on a carrier such that the position of each gemstone is known to preferably about 0.1 mm, and such that the flat back surface of the gemstone is exposed for imprinting. Thus, the faceted / crown portion of the gemstone is attached to the carrier.

At step 740, the flat back surface is treated to prepare the surface for the application of the material that will form the microstructure (or the material that is used as a primer layer to increase adhesion between the material of the gemstone and the material that will form the microstructure). This may include cleaning the surface, for example by mechanical means. Treatment of the surface preferably includes a treatment designed to increase the adhesion between the material of the gemstone and the material of the primer / microstructure. Suitable surface treatment methods include plasma treatments, such as atmospheric plasma treatment, low-pressure plasma treatment, use of a plasma furnace or corona treatment. Amongst these, atmospheric plasma may be particularly advantageous as it may be easier to handle, suitable for in line production, and have high productive efficiency. Optionally, a layer of primer may be applied on the surface to be imprinted, in order to increase adhesion between the surface of the gemstone and the material of the microstructure. Any coating technique known in the art may be used for this, such as printing, spraying, etc. The primer may then be cured, actively or passively, depending on the nature of the primer.

At step 750, a precise amount of imprintable material such as a curable resin is applied on either the flat back surface of the gemstones (NIL) or the working stamps (reverse NIL). Precise dosing of the imprintable material may ensure that the microstructure after imprinting has the appropriate thickness and geometry (which may be compromised if the amount of material is too small); and that no excess material spills out over the edge of the gemstone, which would need to be removed from the product and/or the stamp support / gemstones carrier. Preferably, the amount of curable resin to be dispensed is defined by computing the volume of the desired microstructure and optionally adjusting this amount slightly by experimentation to tailor the amount in view of the specific equipment used. Any technique known in the art for providing curable resin in NIL processes may be used, including screen printing, pad printing, micro-dispensing, flexoprinting, rotary screen printing, inkject printing, roller application, etc. In embodiments, the curable material is applied by screen printing. This technology may benefit from suitable dispensing accuracy while being fast enough for industrial scale production.

At step 760, the layer of imprintable material is imprinted using the working stamp, for example, provided on a roller. Before starting the imprinting process, the decorative bodies on their carrier and the stamps on their support may, if necessary, be aligned by relative movement of the support and carrier, for example using one or more mechanical stop onto which the carrier (or a structure supporting the carrier) can be pushed. Preferably, the microstructure geometry is designed such that rotational alignment between the gemstones and the working stamps is not necessary, as explained above. Also as mentioned above, the imprintable material may be provided on the gemstone (standard NIL) or on the working stamps (reverse NIL, see for example, X. D. Huang, et a!:. Reversal imprinting by transferring polymer from mold to substrate, J. Vac. Sci. Technol., B, Vol. 20, 2078, 2002, the entire content of which is incorporated herein by reference). Reverse NIL may advantageously reduce the risk of bubbles being trapped between the imprintable material and stamp during imprinting, resulting in defects in the microstructure. The distance between the working stamps and the surface of the gemstones is carefully adjusted in order to control the geometry of the microstructure. As mentioned above, the use of elastic / soft materials in the gemstone carrier and/or the stamp support may help to compensate for small deviations from the expected distance between the surface of the gemstone and the stamp.

At the same time or shortly after imprinting, the imprintable material is cured. For example, when the imprintable material is a light (e.g. UV) curable resin, the resin may be cured through the stamp and/or through the support by exposing the resin to electromagnetic (e.g. UV) radiation. Preferably, the imprintable material is cured at the same time as (simultaneously with) imprinting, in order to reduce the risk of reflow of the imprintable material and/or the risk of the imprintable material adhering to the stamp. Suitably, the imprinting material is cured at least partially by exposing the imprintable material to electromagnetic radiation through the support. This may advantageously remove requirements on the stamp to be transparent to the electromagnetic radiation used. In such embodiments, the support is preferably transparent to electromagnetic radiation in a wavelength range suitable for curing the imprintable material (e.g. allowing at least about 50%, at least about 70%, at least about 80%, at least about 90%, at least about 95% or at least about 98% of the radiation within the desired wavelength range to pass through the substrate). Similarly, the gemstone is also preferably transparent to the relevant wavelength of light. Such embodiments may be particularly suitable for use when a transparent substrate (such as e.g. various polymeric films or plates, glass plates etc.) is desirable.

As the skilled person would understand, the method of curing may depend on the imprintable material. In particular, different materials may require different conditions (temperature, humidity, radiation) to cure. Further, some materials may not cure but instead solidify, in which case the material may be imprinted then allowed to solidify. The curable resin may be a UV curable resin, such as a UV curable resin as described further below. In some embodiments, the microstructure is formed by thermal imprinting. Various parameters of the imprinting process may have an impact on the optical properties of the decorative elements of the invention. In particular, the relative position of the gemstone and stamps (as previously discussed), the amount of imprintable material dispensed (as discussed above), the pressure applied between the stamp and the gemstone, the timing of the curing process during imprinting (e.g. timing of start and end of UV exposition, intensity curve between start and end, etc.), the width of focus of the curing radiation light beam (if used), are all controlled. Failure to control these parameters appropriately may result in the presence of air bubbles in the microstructure, an inadequate size or position of the microstructure relative to the gemstone, low surface quality, insufficient adhesion between the microstructure and gemstone / primer, cracks in the microstructure and/or gemstone, reduced stamp life, contamination of the stamp by imprintable material that has not fully cured, problems during demoulding (e.g. due to incomplete or insufficient curing).

At step 770, an at least partially reflective layer is applied. The at least partially reflective layer may have any of the beneficial properties for (partially) reflective layers explained above. In particular, the one or more layers forming the at least partially reflective layer may be applied by physical vapour deposition (PVD) or chemical vapour deposition (CVD), or wet chemical silver coating.

At step 780, a protective layer may be applied on the reflective layer. Any coating technique known in the art may be used for this, such as printing, spraying, etc. The protective layer may then be cured, actively or passively, depending on the nature of the primer. Further layers such as e.g. adhesive layers may additionally be applied, as known in the art.

In other embodiments (not shown), forming a microstructure may comprise providing a mould having concavo-convex structures that are configured to form the facets of the microstructure, combining the gemstone with the mould, and injecting a polymeric material in the space between the mould and the gemstone. In some such embodiments, the gemstone and microstructure can be formed at the same time and/or integrally, for example, using simultaneous injection moulding or injection-compression moulding of plastics. The mould advantageously has a surface roughness Ra below about 100 nm, preferably below about 50 nm, below about 20 nm, below about 10 nm, or below about 5 nm. In embodiments, the mould has a flatness deviation d _f below about 2 pm, preferably below about 1 pm, below about 800 nm, below about 500 nm or below about 200 nm. The decorative elements according to the invention are particularly suitable for use on garments, wearables, fashion accessories, etc. where the combination of a flat back surface as well as the aesthetic potential afforded by the use of a decorative element with improved ‘gem-like’ optical properties are important.

As such, the invention also encompasses an article comprising one or more decorative elements according to the first aspect of the invention. For example, the article may be a clothing accessory such as shoes, a hat, sunglasses, glasses, bags, jewellery (such as a bracelet, a necklace or watch), an electronic wearable (such as an activity tracker, etc.), a piece of clothing (such as a shirt, jacket, jumper etc.), a consumer electronics item (such as a laptop, phone, tablet, etc.), a packaging article (such as a box, can, jar, etc.), or a homeware article (such as a frame, mirror, crockery item, etc).

Other variations of the invention will be apparent to the skilled person without departing from the scope of the appended claims.

Examples

Example 1

In this example, gemstones with flat backs according to the prior art were studied for their optical properties. In particular, gemstones 1000, 1000’ and 1000” made of a material having a refractive index similar to that of crystal glass (i.e. nD = 1.56 ) and having a geometry as illustrated in Figures 8A, 8B, 8C and 8D with a mirror layer on their flat back were simulated using the ray tracing software SPEOS.

Figure 8A shows a schematic front side perspective view of a flat back gemstone 1000 according to the prior art, with a simple cut (referred to as ‘A2000 cut’) comprising a single set of crown facets 1100 extending between a table 1200 and a girdle 1400. Figure 8B shows a schematic front side perspective view of a flat back gemstone 1000’ according to the prior art, with an advanced cut (referred to as ‘A2078 cut’) comprising a first and second set of crown facets 1100’, 1300’ extending between a girdle 1400’ and a flat table 1200’. Figure 8C shows a schematic front side perspective view of a flat back gemstone 1000” according to the prior art, with a simple cut (referred to as ‘A2034 cut’) comprising a single set of crown facets 1100” extending between a table 1200” and a girdle 1400”. Figure 8D shows a schematic front side perspective view of a flat back gemstone 1000”’ according to the prior art, with an advanced cut (referred to as ‘A2038 cut’) comprising a first and a second set of crown facets 1100’”, 1300”’ which alternate around the perimeter of the girdle 1400”’ of the gemstone and extend between the table 1200”’ and the girdle 1400”’.

Figures 8E and 8F show schematic front side perspective and side views of a decorative element 2000 according to the invention, comprising a flat back gemstone 2200 having a generally square profile in plan view. The gemstone 2200 has a generally convex faceted upper surface defined by a plurality of sets of facets 2100, 2100’ and 2100” that vary according to size, shape and angle of inclination relative to the flat back side 2500. The gemstone 2200 has four generally planar side walls 2400 and a flat back side 2500 on which a microstructure 200’ is provided. Whilst Figures 8E and 8F depict a substantially square flat-back gemstone 2200, it will be appreciated the invention encompasses decorative elements comprising gemstones of any suitable size and shape.

With reference to Figure 8A, the gemstone 1000 has a diameter of 3.1 mm; a girdle height of 0.31 mm; and the table 1200 has a shortest diameter of 1.55 mm. Facets 1100 have an angle of 42.0° relative to the plane of the girdle.

With reference to Figure 8B, the gemstone 1000’ has a diameter of 3.1 mm, a girdle height of 0.18 mm height, and the table 1200’ has a shortest diameter of 1.15 mm. Facets 1300’ have an angle of 34.2° relative to the plane of the girdle, and facets 1100’ have an angle of 40.7° relative to the plane of the girdle.

With reference to Figure 8C, the gemstone 1000” has a diameter of 3.1 mm, a girdle height of 0.245 mm height, and the table 1200” has a shortest diameter of 1.242 mm. Facets 1100” have an angle of 25.0° relative to the plane of the girdle.

With reference to Figure 8D, the gemstone 1000”’ has a diameter of 3.1 mm, a girdle height of 0.328 mm height, and the table 1200”’ has a shortest diameter of 1.109 mm. Facets 1100”’, 1300”’ have an angle of 42° relative to the plane of the girdle.

In all cases the table facet 1200, 1200’, 1200” and 1200”’ has an angle of 0° to the girdle plane. The fire and light return of these gemstones 1000, 1000’, 1000”, 1000’” were simulated using the ray tracing software SPEOS, and as explained in Moses et ai, 2004 (Gems & Gemology, Fall 2004, Vol. 40, No. 3, https://www.gia.edu/gems-gemology/fall-2004- grading-cut-quality-brilliant-diamond-moses), as implemented in WO 2015/027252 A1. In particular, for the light return, an illumination arrangement around a hemisphere as illustrated in Figure 2 was used, such that diffuse light irradiates the crown of the gemstones. An observing section on the hemisphere centred on the gemstone and with a symmetrical aperture angle b of 2x1.5°, i.e. 3°, is used to determine the value of the reflected light return with regard to the incident light. This value was then normalised to the value that would be obtained with a corresponding sample of Spectralon®, expressed in %. For the measurement of fire, a directed white light source illuminating the gemstone from the top through an aperture of 2x0.25°, i.e. 0.5° was used. The coloured reflections on an observing surface (a 1 m x 1 m flat observing surface placed parallel to the girdle plane and at 0.5 m above the girdle plane), from the light incident on the gemstone were analysed. In particular, the saturation and illuminance of the reflected light beams were quantified and the fire was quantified as Fire = 100 x ((^(saturation x illuminance)) / (^illuminance)) for each pixel of the observation surface.

The simulated fire and light return were plotted and the results displayed in Figure 9, which shows the quantified fire value (relative to the maximum fire possible) and light return value (relative to the light return of Spectralon®) for the cuts of Figure 8A (A2000), Figure 8B (A2078), Figure 8C (A2034) and Figure 8D (A2038). As can be seen on Figure 9, flat back gemstones according to the prior art have light return values of about 45% for simple cuts like that of Figure 8A, and about 50-70% for advanced cuts such as those of Figures 8B, 8C and 8D. Further, gemstones according to the prior art have fire values in the range of about 30% for simple cuts like that of Figure 8A, and about 35-50% for advanced cuts such as those of Figures 8B, 8C and 8D.

The pattern of light reflections associated with the gemstone of Figures 8A, 8B and 8C were also simulated for shallow, intermediate and steep-angle light, as explained above in relation to Figure 2.

Figures 10A, 10B, 10C and 10D show the pattern of light reflections associated with the gemstone of Figure 8A. Figure 10A shows the pattern of light reflections from shallow angle light, Figure 10B shows the pattern of light reflections from intermediate angle light, Figure 10C shows the pattern of light reflections from steep angle light, and Figure 10D shows the combined light reflections from shallow, intermediate and steep angle light. These figures show that the flat back stone according to the prior art as shown on Figure 8A has poor distribution of light reflections from shallow, intermediate and steep angles. In particular, the gemstone 1000 has about 32% of steep angle light reflection areas (light grey) compared to an ideal of about 15%, with 64% intermediate and 4% of shallow light reflections. Further, the gemstone 1000 comprised a large compact steep-angle light area in the centre of the gemstone (see Figure 10C), and the steep-angle light areas were not distributed in a star-like pattern as would be the case for e.g. a brilliant cut gemstone.

Figures 11 A, 11B, 11C and 11D show the pattern of light reflections associated with the gemstone of Figure 8B. Figure 11A shows the pattern of light reflections from shallow angle light, Figure 11B shows the pattern of light reflections from intermediate angle light, Figure 11C shows the pattern of light reflections from steep angle light, and Figure 11D shows the combined light reflections from shallow, intermediate and steep angle light. These figures show that the flat back gemstone according to the prior art as shown in Figure 8B has improved distribution of light reflections from shallow, intermediate and steep angles compared to the flat back gemstone as shown on Figure 8A, but these remain relatively poor. In particular, the gemstone 1000’ has about 14% of steep angle light reflection areas, with 80% intermediate and 6% of shallow light reflections. The gemstone 1000’ comprised a smaller compact steep-angle light area in the centre of the gemstone (see Figure 11C) compared to gemstone 1000 of Figure 8A, but this was still relatively large (about 1.15-1.2 mm). Additionally, the steep-angle light areas were not distributed in a star-like pattern (see Figure 11C).

Figures 12A, 12B, 12C and 12D show the pattern of light reflections associated with the gemstone of Figure 8C. Figure 12A shows the pattern of light reflections from shallow angle light, Figure 12B shows the pattern of light reflections from intermediate angle light, Figure 12C shows the pattern of light reflections from steep angle light, and Figure 12D shows the combined light reflections from shallow, intermediate and steep angle light. These figures show that the flat back gemstone according to the prior art as shown in Figure 8C has worse distribution of light reflections from shallow, intermediate and steep angles compared to the flat back gemstones as shown on Figures 8A and 8B, which are themselves relatively poor. In particular, the gemstone 1000” has about 15% of steep angle light reflection areas, with 79% intermediate and 4% of shallow light reflections. The gemstone 1000” comprised a large compact steep-angle light area in the centre of the gemstone (see Figure 12C) compared to gemstone 1000 of Figure 8A, and gemstone 1000’ of Figure 8B. Additionally, the steep-angle light areas were not distributed in a star-like pattern (see Figure 12C).

The light reflection data therefore indicates that these flat back gemstones according to the prior art tend to have poor optical properties compared to brilliant cut gemstones.

Example 2

In this example, the inventors sought to improve on the flat back gemstones of the prior art (Example 1), by providing decorative elements according to the invention, which combine the gemstones of the prior art with a microstructure and reflective layer. Microstructure geometry was designed to optimise the brilliance (fire and light return) of the decorative element for each gemstone cut.

Figure 13A shows a perspective view of a microstructure according to an embodiment of the invention. Figure 13B is a diagram that shows the pattern of grooves that was used to create the geometry shown on Figure 13A. In particular, nine identical triangular grooves with a first planar wall inclined at an angle of 5.4° and a second planar wall inclined at an angle of 14.6° were created. Each groove was located with the first planar wall nearer the centre of the microstructure, and at a distance l_ _R from the centre of the structure, where l_ _R is equal to 64.5% the radius of the microstructure. Each groove was rotated by 40°, producing a pattern that has nine-fold rotational symmetry. The microstructure shown on Figure 13A was combined with the gemstone shown on Figure 8A, resulting in the decorative element shown on Figure 14 when view in white light. The resulting decorative element has a light return of 68.1% and a fire of 40.6% - compared to about 45% and about 30%, respectively, for the corresponding flat back gemstone according to the prior art (see Figure 9).

Figures 15A, 15B, 15C and 15D show the pattern of light reflections associated with the decorative element of Figure 14. Figure 15B shows the pattern of light reflections from shallow angle light, Figure 15C shows the pattern of light reflections from intermediate angle light, Figure 15D shows the pattern of light reflections from steep angle light, and Figure 15A shows the combined light reflections from shallow, intermediate and steep angle light. These figures show that the decorative element of the invention has an improved distribution of light reflections from shallow, intermediate and steep angles compared to the corresponding gemstone of the prior art. In particular, the decorative element of Figure 14 has about 13.2% of steep angle light reflection areas (compared to an ideal of about 15%, and about 32% for the gemstone of Figure 8A), with 82.2% intermediate and 4.6% of shallow light reflections (compared to 64% and 4% for the gemstone of Figure 8A). Whilst the total amount of light return is not necessarily significantly higher than for the corresponding prior art gemstone at all angles (shallow, medium, high), the distribution of light return for the gemstone of the invention (Figure 14) is more visually pleasing, in comparison to the prior art, as is clear from the comparison of Figures 10A to 10D against Figures 15A to 15D for the gemstone of the invention.

Figure 16A shows a perspective view of a microstructure according to an embodiment of the invention. Figure 16B is a diagram that shows the pattern of grooves that was used to create the geometry shown on Figure 16A. In particular, nine identical triangular grooves with a first planar wall inclined at an angle of 8.2° and a second planar wall inclined at an angle of 4.9° were created. Each groove was located with the first planar wall towards / nearest the centre of the microstructure, and at a distance l_ _R from the centre of the structure equal to 88.6% the radius of the microstructure. Each groove was rotated by 40°, producing a pattern that has nine-fold rotational symmetry. The microstructure shown on Figure 16A was combined with the gemstone shown on Figure 8C, resulting in the decorative element shown on Figure 17 when view in white light. The resulting decorative element has a light return of 68.0% and a fire of 40.91% - compared to about 55% and about 45%, respectively, for the corresponding flat back gemstone according to the prior art.

Figures 18A, 18B, 18C and 18D show the pattern of light reflections associated with the decorative element of Figure 17. Figure 18B shows the pattern of light reflections from shallow angle light, Figure 18C shows the pattern of light reflections from intermediate angle light, Figure 18D shows the pattern of light reflections from steep angle light, and Figure 18A shows the combined light reflections from shallow, intermediate and steep angle light. These figures show that the decorative element of the invention has an improved distribution of light reflections from shallow, intermediate and steep angles compared to the corresponding gemstone of the prior art. In particular, the decorative element of Figure 17 has about 2.7% of steep angle light reflection areas (compared to about 15% for the gemstone of Figure 8C), with 87.7% intermediate and 9.6% of shallow light reflections (compared to 79% for intermediate and 4 % for shallow light reflections for the gemstone of Figure 8C). Whilst the total amount of light return is not necessarily significantly higher than for the corresponding prior art gemstone, the distribution of light return for the gemstone of the invention (Figure 17) is significantly more visually pleasing, giving the impression of a brilliant cut gemstone in comparison to the prior art, as is clear from the comparison of Figures 12A to 12D against Figures 18A to 18D for the gemstone of the invention. In particular, the gemstone of the invention produces a star- like light reflection pattern with reduced size central high-reflection region.

Figure 19A shows a perspective view of a microstructure according to an embodiment of the invention. Figure 19B is a diagram that shows the pattern of grooves that was used to create the geometry shown on Figure 19A. In particular, six identical triangular grooves with a first planar wall inclined at an angle of 5.3° and a second planar wall inclined at an angle of 7.9° were created. Each groove was located with either the first planar wall or the second planar wall towards the centre of the microstructure, i.e. within each pair of parallel grooves 280a, 280b, one 280b has the first planar wall towards the centre (indicated by a dashed line on Figure 19B), and one 280a has the second planar wall towards the center (indicated by a solid line on Figure 19B). Each groove was located at a distance l_ _R from the centre of the structure equal to 64.5% the radius of the microstructure. Each groove was rotated by 60°, producing a pattern that has three-fold rotational symmetry (due to the alternating orientation of the grooves). The microstructure shown on Figure 19A was combined with the gemstone shown on Figure 8B, resulting in the decorative element shown on Figure 20. The resulting decorative element has a light return of 60.44% and a fire of 48.26% - compared to about 55% and about 48%, respectively, for the corresponding flat back gemstone according to the prior art.

Figures 21 A, 21 B, 21 C and 21 D show the pattern of light reflections associated with the decorative element of Figure 20. Figure 21 B shows the pattern of light reflections from shallow angle light, Figure 21 C shows the pattern of light reflections from intermediate angle light, Figure 21 D shows the pattern of light reflections from steep angle light, and Figure 21A shows the combined light reflections from shallow, intermediate and steep angle light. These figures show that the decorative element of the invention has an improved distribution of light reflections from shallow, intermediate and steep angles compared to the corresponding gemstone of the prior art. In particular, the decorative element of Figure 20 has about 9% of steep angle light reflection areas (compared to about 14% for the gemstone of Figure 8B), with 81.5% intermediate and 9.5% of shallow light reflections (compared to 80% and 6% for the gemstone of Figure 8B). Further, as can be seen on Figure 21A, the decorative element according to the invention does not show a dark ring in the light reflection from steep angles in comparison to the gemstone of the prior art (See Figure 11C). Whilst the total amount of light return is not necessarily significantly higher than for the corresponding prior art gemstone at all angles of reflection, the distribution of light return for the gemstone of the invention (Figure 20) is significantly more visually pleasing, as is clear from the comparison of Figures 12A to 12D against Figures 21A to 21 D for the gemstone of the invention. In particular, the gemstone of the invention produces a more star-like light reflection pattern with reduced size central high-reflection region.

Figure 22A shows a plan view of a microstructure according to another embodiment of the invention. Figures 22B and 22C show the stamp parts that were used to create the geometry shown on Figure 22A. In particular, a faceted pyramid with 7-fold rotational symmetry and a radius of 63.8% of the radius of the gemstone was combined with a flat outer ring. The latter part can for example be obtained using a monocrystalline diamond tool, as explained above. Each of the facets of the pyramid had an angle of 11.2° relative to the flat back surface of the gemstone. The microstructure shown on Figure 22A was combined with the gemstone of Figures 8A, 8B and 8C. Figure 23 shows the appearance of a gemstone according to Figure 8B combined with the faceting arrangement of Figure 22A. The resulting decorative element has a light return of 39.36% and a fire of 46.03% - compared to about 55% and about 48%, respectively, for the corresponding flat back gemstone according to the prior art.

Figures 24A, 24B, 24C and 24D show the pattern of light reflections associated with the decorative element of Figure 23. Figure 24B shows the pattern of light reflections from shallow angle light, Figure 24C shows the pattern of light reflections from intermediate angle light, Figure 24D shows the pattern of light reflections from steep angle light, and Figure 24A shows the combined light reflections from shallow, intermediate and steep angle light. These figures show that the decorative element of the invention has an significantly improved distribution of light reflections from shallow, intermediate and steep angles compared to the corresponding gemstone of the prior art. In particular, the decorative element of Figure 23 has about 24.8% of steep angle light reflection areas (compared to about 14% for the gemstone of Figure 8B), with 68.4% intermediate and 6.8% of shallow light reflections (compared to 80% and 6% for the gemstone of Figure 8B). Further, as can be seen on Figure 24A, the decorative element according to the invention does not show a dark ring in the light reflection from steep angles, as did the gemstone of the prior art (see Figure 11C). Further, the decorative element according to the invention also does not comprise a complicated pattern on the outer ring of the gemstone. This can be aesthetically advantageous.

Embodiments of the invention are set out in the following numbered clauses:

1. A decorative element comprising: a decorative body with a back surface, a microstructure on the flat back surface of the decorative body, wherein the microstructure comprises a faceted region, and an at least partially reflective layer on at least a portion of the faceted region of the microstructure; wherein the combination of the faceted region and the at least partially reflective layer is configured to reflect light incident on the at least partially reflective layer through the decorative body and/or microstructure; optionally, the decorative body is a faceted decorative body; optionally the back surface is a flat back surface; beneficially light incident on the at least partially reflective layer is reflected through the decorative body and/or microstructure in multiple directions.

2. The decorative element of Clause 1, wherein the microstructure has a height of less than 1,000 pm, less than 500 pm, less than 300 pm, less than 200 pm; and/or at least 10 pm, at least 20 pm, at least 30 pm, at least 40 pm or at least 50 pm or at least 100 pm.

3. The decorative element of Clause 1 or Clause 2, wherein the faceted region is created by concave faceted portions of the microstructure.

4. The decorative element of any preceding clause, wherein the concave faceted portions of the microstructure have a depth of between 1 pm and 1,000 pm, between 5 pm and 500 pm, between 10 pm and 400 pm, between 20 pm and 300 pm, between 30 pm and 200 pm, or between 40 pm and 100 pm.

5. The decorative element of any preceding clause, where the facets in the faceted region are each inclined relative to the flat back surface of the faceted decorative body by an angle between 1° and 30°, between 2° and 25°, between 3° and 20°, or between about 4° and about 16°; optionally wherein each of the facets is inclined related to the flat back surface of the faceted decorative body by substantially the same angle, or wherein the angles between the facets in the faceted region and the flat back surface of the faceted decorative body are selected from one of two angles. 6. The decorative element of any preceding clause, wherein the faceted region of the microstructure comprises a plurality of facets in the shape of a pyramid, wherein each facet is formed of a planar wall of the pyramid, and the angle between each of the planar walls of the pyramid and the flat back surface of the decorative body is individually selected from between 1° and 30°, between 2° and 25°, between 3° and 20°, or between 4° and 16°; preferably, wherein the angle is the same for each facet of the pyramid.

7. The decorative element of Clause 6, wherein the pyramid has between 4 and 13 planar sides, between 5 and 12 planar sides, or between 6 and 11 planar sides; optionally wherein the facets of the pyramid are of equal size, or wherein the facets of the pyramid are of two or more different sizes.

8. The decorative element of any of Clauses 1 to 5, wherein the faceted region of the microstructure comprises a plurality of grooves creating a pattern of facets wherein the grooves comprise two planar walls, and the angle between each of the planar walls of the grooves and the flat back surface of the decorative body are individually selected from between 1° and 30°, between 2° and 25°, between 3° and 20°, or between 4° and 16°.

9. The decorative element of Clause 8, wherein the plurality of grooves are rotated relative to each other by: (i) a constant angle about a centre point of the decorative body, and are located relative to each other to form an n-fold rotational symmetrical pattern; or (ii) two or more different angles about a centre point of the decorative body, and the plurality of grooves define a pattern having rotational symmetry where the degree of rotational symmetry is less than the number of grooves.

10. The decorative element of any preceding clause, wherein the faceted region comprises a pattern of facets that has n-fold rotational symmetry.

11. The decorative element of Clause 10, wherein the faceted decorative body has m-fold rotational symmetry, and m is a different integer to n.

12. The decorative element of any preceding clause, wherein the facets of the microstructure are planar surfaces with low surface roughness and a high degree of flatness; optionally wherein the surface roughness is below 100 nm, below 50 nm, below 20 nm, below 10 nm, or below 5 nm, and/or the flatness has a flatness deviation d _f below 2 pm, below 1 pm, below 800 nm, below 500 nm or below 250 nm.

13. The decorative element of any preceding clause, wherein the microstructure is formed from a layer of material applied on the flat back surface of the faceted decorative body; or wherein the microstructure is formed integrally with the faceted decorative body; optionally wherein the faceted portion of the microstructure is formed by imprinting the flat back surface of the faceted decorative body or a layer or material applied on the flat back surface of the faceted decorative body, such as by imprint lithography.

14. The decorative element of any preceding clause, wherein the microstructure and/or the decorative body is/are made from a transparent material.

15. The decorative element of any preceding clause, wherein the faceted decorative body is a gemstone; optionally wherein the gemstone is made of glass, crystal glass, glass ceramic, plastic or cubic zirconium.

16. The decorative element of any preceding clause, wherein the flat back surface of the decorative body has a diameter of between 1 mm and 250 mm, between 1 mm and 150 mm, between 2 mm and 120 mm, between 2 mm and 100 mm, between 3 mm and 80 mm or between 3 mm and 60 mm; and/or wherein the decorative body has a height between 1 mm and 120 mm, between 1 mm and 100 mm, between 2 mm and 80 mm, or between 2 mm and 60 mm.

17. The decorative element of any preceding clause, further comprising one or more protective layers on the at least partially reflective layer; and/or optionally further comprising an adhesive layer on the protective layer.

18. The decorative element of any preceding clause, wherein the microstructure is made from a material that has a refractive index that is similar to, such as within 30%, within 20%, within 10% or within 5% of that of the material of the decorative body.

19. A method of making a decorative element, the method comprising: providing a decorative body having a back surface; forming a microstructure on the back surface of the decorative body, wherein the microstructure comprises a faceted region; forming an at least partially reflective layer on at least a part of the faceted region of the microstructure, wherein the combination of the faceted region and the at least partially reflective layer is configured to reflect light incident on the at least partially reflective layer through the decorative body and/or microstructure; optionally, the decorative body is a faceted decorative body; optionally the back surface is a flat back surface; beneficially light incident on the at least partially reflective layer is reflected through the decorative body and/or microstructure in multiple directions.

20. The method of Clause 18, wherein forming a microstructure comprises applying a layer of imprintable material and imprinting a microstructure into the layer of imprintable material using a stamp; optionally wherein the method further comprises curing the imprintable material. 21. The method of Clause 20, wherein the method further comprises providing a working stamp by replicating a master stamp into a polymeric stamp material; optionally wherein the master stamp is a metallic master stamp, a hard metal master stamp or a non-metallic master stamp; and/or wherein the working stamp has low surface roughness and high flatness.

22. The method of Clause 21, comprising providing a metallic or non-metallic master stamp, wherein providing a metallic or microcrystalline master stamp comprises creating a plurality of facets in a metal or microcrystalline substrate; optionally using a monocrystalline diamond cutting tool; optionally wherein the monocrystalline diamond cutting tool has a non-symmetrical triangular cutting profile.

23. The method of Clause 22, wherein creating a plurality of facets in a metal or microcrystalline substrate comprises creating a plurality of grooves with a monocrystalline diamond cutting tool, wherein the grooves have a V-shape corresponding to the shape of the monocrystalline diamond cutting tool.

24. The method of Clause 22 or Clause 23, wherein a single monocrystalline diamond cutting tool profile is used to create all of the grooves.

25. The method of Clause 22, wherein creating a plurality of facets in a metal or microcrystalline substrate comprises creating a plurality of facets defining a pyramid in the substrate.

26. The method of any of Clauses 20 to 25, wherein imprinting a microstructure into the layer of imprintable material using a stamp comprises providing a plurality of stamps on a support; and providing a faceted decorative body comprises providing a plurality of decorative bodies on a carrier; optionally wherein the support and/or the carrier comprise an elastomeric material.

27. The method of any of Clauses 19 to 25, wherein providing a faceted decorative body comprises providing a plurality of faceted decorative bodies and positioning the decorative bodies on a carrier by sieving the decorative bodies; optionally transferring the sieved decorative bodies onto a centring plate, and transferring the decorative bodies onto the carrier.