This invention relates to translucent stone cluster effect articles such as might comprise jewellery, objects de vertu or objets d'art, and which include glassware such as tumblers, stemware, carafes, vases and decanters.

Jewellery features precious and semi-precious stones, most often transparent, and faceted to sparkle by splitting light into rainbow colours or reflecting light from the facets.

Precious stones are characterised by high refractive index, more effective at sparkling, but semi-precious stones, glass, particularly flint glass, and even plastics, particularly acrylics, can be used to good effect.

The 'cut' of a precious or semi-precious stone, its finished shape, is to some extent dictated by its crystal structure presenting preferred lines of cleavage, but the lapidary also has regard to hiding imperfections and the way light is refracted and reflected by the faceting, and, of course, the way the stone fits into the design of the piece in which it is to be mounted. Classic cuts include round, baguette, rose, heart, princess, and these are copied into glass and plastic, the general idea being to make the cheaper 'stones' resemble the precious stones as closely as possible.

The back of a stone, known as the 'pavilion' is of importance for the sparkle as the front, or 'crown' - the pavilion is where light incident on the crown is internally reflected so that it emerges from the crown after diffraction. The crown, the front of the stone, is where the light is refracted, and split into colours because of the different refractive indices for different wavelengths.

Stones, of whatever material, are conventionally mounted in a piece of jewellery, a ring, a brooch, a pendant, which must have provision for holding stones securely and without impeding the sparkle, and this is important when stones are clustered. The usual cluster mount involves claw structures, comprising two or four claws per stone, which should, in many designs, when the piece is assembled, be barely visible, or not visible at all - termed a pave setting. Making these structures fine, as particularly in grain setting, or micro pave setting, but strong, so that stones do not fall out, especially in soft metals such as gold and silver, involves intricate craftsmanship.

Stone clusters, precious or otherwise, also feature in decorative objects, not necessarily for personal adornment, such as etuis, decorated 'eggs', and also handbags, shoes, wallets, sunglasses, belt buckles, and like objects that can be classed as miniature objets de vertu and objets d'art. Glassware, such as decanters and drinking glasses are cut into patterns, one well-known such being a pave effect of pyramids.

The present invention provides new ways for creating optical effects in jewellery, miniature objets de vertu and objets d'art, and glassware. The invention comprises a translucent stone cluster effect article having substantially parallel front and back faces, comprising a relief pattern of faceted projections on its back face, the front face being unfaceted, the faceted projections comprising close packed prisms or right pyramids with even numbers of sides with an apex angle of between 80° and 100°.

Such a pattern of projections gives rise to a novel and unexpected effect when viewed with the front face towards the observer - the article appears particularly bright, due to total internal reflection of light coming from behind the observer straight back towards the observer - retroreflection.

When viewed with the back face towards the observer, this retroreflection brightness is not observed, but the facets of the projections reflect light coming from other directions to give a sparkling effect, so that it works as a piece of jewellery viewed from either side. As a monolithic piece, cut, for example, from a single piece of cubic zirconia (CZ), there is no need of a mount, except provision, as by a drilling or a bail, for a cord or chain for a necklace or bracelet, but, if a mount is provided, it can also be reversible.

By 'close packed' is meant contiguous or substantially so, with gaps between the bases of the pyramids less than one fifth the pyramid base length, which makes the most use of the faceted region. To maximise the retroreflective effect, the prisms or pyramids may be full rather than truncated, though may have a small culet to protect against damage.

The pyramids may be four sided.

The apex angle may be between 86° and 90°, with an angle between 89° and 91° being particularly effective.

The front face may be flat or it may have a shallow convex or concave curvature. By 'shallow' is meant the depth at the centre, for a convex surface is no more than twice the average depth, and for a concave surface, the depth at the centre is greater than half the average depth.

The faceting need not extend to the edges of the article, so that a monolithic article has an unfaceted rim, giving the appearance of a mount. A monolithic article may in any event have a rim e.g. of metal, e.g. gold or other precious or semiprecious metal, giving the appearance of a mount holding a pave setting if individual stones, and such rim may have a loop for a chain or a brooch or other mount. However, faceting may extend up to at least one edge of the article, giving a jagged edge, well-nigh impossible in conventional pave designs. A monolithic article, with no mount, may be pierced for a chain or cord. Typical shapes for such articles include rectangular, elliptical, heart-shaped and tear drop.

The apexes may be spaced apart by 2.1 mm, 2.7 mm or 3.5 mm, which spacings are found to have desirable optical effects, but, of course, other spacings can be used, and a single article may have graded or irregular spacings. However, it is possible also to emulate microsetting of pave designs by using a spacing as fine as 1mm. The article may be of a transparent material, which may be CZ. CZ has a refractive index of 2.15, which means that a ray striking the surface at an angle of incidence greater than about 28° will be totally internally reflected. If the light is totally internally reflected twice, so that it emerges from the front face, this retroreflection will give articles an unusually bright appearance almost regardless of the illumination conditions.

While glassware is, as mentioned above, already cut with a pattern of pyramids, this is always on the outer face. It would be well-nigh impossible, in any reasonable manufacturing context, to put such a pattern on the inner face of a decanter, for example. Some glassware is cut, usually with a 'star' pattern, on its base, which does not, of course, achieve an overall retroreflective effect, because usually the cut is at around 60° to the surface, and because the cuts fan out from the centre, leaving most of the base area for light to pass straight through without reflection.

The invention also comprises a method for making a monolithic stone cluster effect article, comprising cutting grooves into one face of a disc of material to form an array of close packed prisms or right pyramids with an apex angle of between 80° and 100°. Preferred angles are between 84° and 96°, particularly between 89° and 91°.

The method may be used to cut articles from translucent or transparent materials such as glass and CZ for jewellery pieces, which will, viewed on the uncut face, exhibit retroreflection due to total internal reflection from the facets of the prisms or from even- sided pyramids.

The method may also be used on opaque material to give a faceted monolith of any desired size and shape, which may, with a simple mount or even with no mount at all, be used as a piece of jewellery.

Two sets of grooves may be cut at right angles to form four sided pyramids.

The grooves may be cut by a multi-bladed cutting wheel, in which, particularly for a hard material like CZ, the blades may be coated with a diamond grit, other grits, such as carborundum, serving for less hard substances.

The cutting wheel may itself be fashioned from a master cutting wheel, which can be used to make many replacement wheels. The facets may be polished after cutting, enhancing their total internal reflection property. This may be done by hand or with a like cutting wheel with very fine grit.

Optical effects may be achieved by coating the projections, for example, by silvering them, which is usually done by applying a layer of aluminium, which may improve reflectivity, or, especially in the case of CZ, by vacuum deposition of diamond, which may temper dispersion. Translucent stone cluster effect articles and methods for making them according to the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a rear view of one, heart-shaped, article;

Figure 2 is a section on the line II- II of Figure 1 ;

Figure 3 is a section like Figure 2, but of an article with a shallow convex front surface;

Figure 4 is a diagrammatic section through a part of the article of Figures 1 and 2, showing a totally internally reflected ray; Figure 5 is a section like Figure 4, through a part of the article of Figure 3;

Figure 6 is a view of an article like that of Figure 1, but of square shape;

Figure 7 is a view of an article like that of Figure 1, in a tear drop shape;

Figure 8 is a view like Figure 6 of an article with graded apex spacing;

Figure 9 is a view like Figure 6 of an article with an inset stone; Figure 10 is a diagrammatic illustration of a manufacturing set-up;

Figure 11 is a side elevation of a tumbler;

Figure 12 is a view in the direction of Arrow 12 on Figure 11;

Figure 13 is a side elevation of a stemmed glass;

Figure 14 is a view in the direction of Arrow 1 4 of Figure 13; Figure 15 is a part section through the base of a prior art, conventionally star cut glass, showing light paths;

Figure 16 is a part section like Figure 15 of a cut glass base of a glass like those of

Figures 11 to 14;

Figure 17 is a side elevation of a bracelet with a pave applique;

Figure 18 is a view on Arrow 18 of Figure 17, to a larger scale; Figure 19 is a section through the pave section of the bracelet of Figures 16 and 17, with a prior art pave applique; Figure 20 is a section like Figure 19 with a pave applique according to the invention;

Figure 21 is a view of the base of a second embodiment of stemmed glass with a different pave design;

Figure 22 is a section on the line 22-22 of Figure 21; and

Figure 23 is a view like Figure 21 of the base of a third embodiment of stemmed glass with a further pave design.

The drawings illustrate comprises a translucent stone cluster effect article 11 having substantially parallel front and back faces 12, 13 respectively, comprising a relief pattern of faceted projections 14 on its back face 13, the front face 12 being unfaceted, the faceted projections 14 comprising close packed right pyramids with even numbers of sides with an apex angle of between 80° and 100°.

Such an article has an unusually bright appearance when viewed from the front, as it retroreflects light coming from behind the observer due to two total internal reflections from opposite facets of the projections 14.

By 'close packed' is meant contiguous or substantially so, with gaps between the bases of the pyramids less than one fifth the pyramid base length. Gaps reduce the area over which incident light is retroreflected and hence the brightness of the article.

The pyramids 14 are four-sided, but six- and eight-sided pyramids are possible, though more difficult to cut. The pyramids as illustrated are pointed, but could have a small flat - a culet in gemstone parlance - in case the article is to be worn as a pendant, when points might irritate. The culet is desirably small as it, too, reduces the area over which light is retroreflected.

Generally, the closer the apex angle is to 90° the better. An apex angle between 86° and 94° works very well, with an angle between 89° and 91° being particularly effective. Figures 1, 2 and 4 illustrate an article 11 of which the front face 12 is flat, while Figures 3 and 5 illustrate an article 11 of which the front face 12 has a shallow convex curvature. An article could also have a shallow concave front face. By 'shallow' is meant the depth at the centre, for a convex surface, is no more than twice the average depth, and for a concave surface, the depth at the centre is greater than half the average depth. . With a convex or concave front face 12, as seen in Figure 5, rays coming in from the side are refracted at the face 12 and presented to the facets so that they are retroreflected.

Figure 1 illustrates an article 11 in which the faceting does not extend to the edges of the article, so that the article 11 has an unfaceted rim 11a, giving the appearance of a mount. An article 11 can in any event have a metal, e.g. gold or other precious or semiprecious metal, giving the appearance of a mount holding a pave setting. The article 11 of Figure 6 has edgewise bars 1 lb that could clamp the article 11 to comprise a brooch or pendant. In the article of Figure 6 however, faceting extends up the two edges of the article not bounded by the bars 1 lb, giving jagged edges 1 lc. Figures 1, 2 and 4 illustrate an article 11 of which the front face 12 is flat. Figures 3 and 5 illustrate an article with a shallow convex front face 12. By 'shallow' is meant the depth at the centre, for a convex surface is no more than twice the average depth, and for a concave surface, the depth at the centre is greater than half the average depth. The curvature will alter the appearance of the back face projections, as seen through the front face 12, and will alter the zone from and into which rays are retroreflected as a result of refraction at the front face 12.

The apexes 14 can be spaced apart by 2.1 mm, 2.7 mm or 3.5 mm, which spacings are found to have desirable optical effects, but, of course, other spacings can be used, and a single article may have graded or irregular spacings. Figure 8 illustrates an article 11 with graded spacing. However, it is possible also to emulate microsetting of pave designs by using a spacing as fine as 1mm.

The article 11 can, and will usually be of a transparent material, which may be cubic zirconia (CZ). CZ has a refractive index of 2.15, which means that a ray striking the surface at an angle of incidence greater than about 28° will be totally internally reflected. This will give articles an unusually bright appearance almost regardless of the

illumination conditions. Articles which are translucent, but not transparent, will display retroreflectivity, but the effect will be more diffuse, depending on the extent to which the article is not fully transparent.

Figure 9 illustrates an article 11 in which the simulated pave is used as a setting for a precious or semiprecious stone 15, which might, otherwise, for example, be a pearl, an enamel insert.

Figure 10 illustrates a method for making a stone cluster effect article, comprising cutting intersecting grooves into one face of a disc 101 of translucent material to form close packed right pyramids with even numbers of sides with an apex angle of between 84° and 96°, preferably between 89° and 91°.

The disc 101, which may be of any size and shape, is shown held by a clamp arrangement 102 on a rotatable table 103 and held steady while a rotating multi-bladed cutting wheel 104 is traversed across it to leave close-packed grooves. Two sets of grooves may be cut at right angles to form four sided pyramids.

The wheel, in which, particularly for a hard material like CZ, the blades may be coated with a diamond grit. The cutting wheel 104 is itself fashioned from a master cutting wheel and, in a production facility, replaced when worn with another, again fashioned from the master. When working with cubic zirconia, wheels will typically need to be replaced after one hundred cutting operations.

The facets can be polished after cutting, enhancing their total internal reflection property, either by hand, using a fine grit, or using a fine grit wheel. The surface of the article 11, particularly when of CZ, can be vacuum coated with diamond, as is sometime done to reduce the 'fire' of the stone due to its high dispersion, or it can be silvered, which may aid retroreflection, protect the facets or, in the case of a reversible item, provide an attractive finish.

Two sets of grooves are cut at right angles to form four sided pyramids, and this will normally suffice, but more cuts can be made to yield pyramids with more faces, even- numbered if retroreflectivity is required. Typical shapes for such articles include rectangular, Figures 6, 8 and 9, elliptical, heart- shaped, Figure 1, and tear drop, Figure 7. The size of articles that can be made as described is limited only by the size of the blank or disc from which they are fashioned. CZ can be made in discs up to 34cm in diameter, and, with suitable equipment, a cluster effect article can be made from CZ up to that size. Using other materials such, for example, as glass crystal, even larger pieces can be made. Opaque materials can be used to make pave effect monolithic articles displaying the facets. One or two examples of opaque materials being used in this way are known, but only in small, earring sized articles, seemingly moulded to have only four projections, these being of truncated pyramid form.

Figures 11 to 24 of the drawings illustrate pave effect articles 11 made of glass which at least in part comprise substantially parallel front 12 and back 13 faces, the back face 13 comprising a relief pattern of faceted projections 14, the front face 12 being unfaceted, the faceted projections 14 comprising close packed right pyramids with even numbers of sides with an apex angle between 80° and 100°.

The front face 12 is, of course, the face from which the article 11 is viewed, and is the technical back, as referred to above. Thus the front face 12 of the tumbler 11 illustrated in Figures 11 and 12 is the upper or inner surface of the base of the tumbler as will be viewed from above when the tumbler is on a table or when it is raised for drinking. The retroreflective effect will be but little affected by the presence of liquid in the tumbler, as the faces involved in total internal reflection will not be in the liquid.

The front face 12 of the stemmed glass 11 illustrated in Figures 13 andl4 is the upper face of the foot of the glass, which will likewise be seen when the glass is on a table or raised for drinking.

The apex angle can be between 89° and 91 - desirably as close to 90° as possible for maximum brilliance. The number of sides of the pyramidal projections 14 illustrated is four - six or eight would work, but would be more difficult to make. The article 11 can be any conventional article of glass that affords the substantially parallel front and back faces 12, 13. Thus an article of glassware, such as a tumbler, stemmed glass, carafe, jug or decanter will have a base which will normally be viewed, when the article is standing on it, from above. When so viewed, the faceted area will appear brilliant because of the light incident on the upper face 12 being retroreflected towards the viewer.

The whole of the back face 13 of the base of the tumbler 11 of Figures 11 and 12 is faceted. The stemmed glass 11 of Figures 13 and 14 is just part faceted in a four pointed star design, but of course any other design can be applied, such as a circle, an ellipse, crossed ellipses, a square, a triangle, a five or six pointed star, a heart shape, or more complex shapes such as company or club logos, animals, flowers, indeed, any shape that can be devised that will permit of being realised in the faceting. The faceting can be effected in any appropriate size, for example with a spacing between apexes of the pyramidal projections 14 of 3.5 mm, 2.7 mm, 2.1 mm or less. Where the article rests on its base, it may be desirable that the points of the faceting are elevated, and the faceting may be done, then, within a rim, or the base may be concave to that end. The projections 14 of the tumbler of Figures 11 and 12 are recessed within a rim 15. The front face 12 of the tumbler 11 is flat, while that of the stemmed glass 11 of Figures 13 and 14 has a shallow convex curvature. By 'shallow' is meant the depth at the centre, for a convex surface is no more than twice the average depth. A concave surface, such as might be the inner face of a tumbler, decanter, vase or the like, could have a depth at the centre greater than half the average depth. And, as already mentioned, 'substantially parallel' does not exclude that one face may be flat while the other is curved or that they may be oppositely curved.

By 'close packed' is meant contiguous or substantially so, with gaps between the bases of the pyramidal projections 14 less than one fifth the pyramid base length. For maximum retroreflection there should be no gap at all. Nor, again, for maximum brilliance, should the pyramidal projections 14 be truncated, though tiny culets could militate against wear of or damage to or by points.

Figures 15 and 16 illustrate the different effects of the conventionally star cut base (Figure 15) and the cut according to the invention. In the prior art, conventionally cut base of Figure 15, most of the base is flat, and light incident on the front face 12 mostly passes straight through, possibly retroreflecting off neighbouring surfaces of radial cuts, if the apex angles are right, which they seldom are, usually being around 120°. In the case of figure 16, cut according to the invention, it is seen that substantially all the light is retroreflected.

As mentioned above, pave effects in jewellery are effected by assembling individual stones. In common with other jewellery comprising gemstones, the crowns of the stones are exposed on the outer or front face. GB2492225 discloses the production of pave jewellery by punching, machining or otherwise working the outer face of a workpiece, or by an additive process such as 3D printing, but, again, to put the relief pattern on the exposed face.

Figures 17 and 18 illustrate a bracelet 71 with a pave applique 11. Prior art pave appliques would comprise individual gemstones or glass crystals 73, as seen in the cross section of Figure 19, in some kind of mount, not shown. The gemstone crowns are on the front face, and they will, depending on the direction of incident light, reflect light from their facets or allow it to pass into the gemstone undergoing refraction and dispersion, and some, but by no means all, of the light will be totally internally reflected to emerge from one or other of the front face facets, where it will be further refracted and dispersed - a discussion of this is to be found in US2015/0201720, D. Swarovski AG.

By contrast, in the pave applique shown in cross section in Figure 20, the front face 12 is unfaceted, so that, with light incident from behind the viewer there is substantially no front face reflection away from the viewer, the majority of the light passing straight through substantially without refraction or dispersion to be totally internally reflected off opposite faces of the rear face 13 faceting to be retroreflected back towards the viewer for maximum brilliance. Aside from the brilliant effect, and advantage of this is that the front face is smooth and does not collect dirt, while the faceted face can be sealed in a mount.

For jewellery or objets d'art applications, of course, harder glass-like materials can be used, such as cubic zirconia, which can be obtained in appropriated sizes.

Of course, the bracelet could be made so as to have the facets on the outer face, resembling the bracelet of Figure 19, but with a monolithic 'stone' in which facets resemble the pave cluster of individual stones, without requiring a mount holding the individual stones.

Figures 21 and 22 illustrate a stemmed glass 11 of which the underside 13 of the foot has parallel grooves leaving prismatic projections 14. While this is superficially similar to a star cut often found on quality crystal glassware, the grooves on such glassware usually have a much more obtuse included angle, usually about 120° and, while close together at the centre, spread out so that they do not define prisms, and there is no possibility of total internal reflection. Light reflected off the faces of the grooves can give the base a flash of brilliance, but only, usually, from one, at most a couple of grooves when incident light is at an appropriate angle. Figure 23 illustrates a design in which the parallel projections 14 are circular. Again, light will be totally internally reflected off the inner faces of the projections 14 to be redirected out of the front face 12 for a bright, retroreflective appearance. Instead of being parallel circular projections, a spiral groove could be cut leaving a single spiral projection which sufficiently satisfies the requirements of close packing and parallelism for the purposes of the invention. The faceting can be effected by any of the usual methods, as by cutting and polishing, etching, or by moulding. Polishing enhances the retroreflective effect by enhancing the total internal reflection. Optical effects may be achieved by coating the projections, for example, by silvering them, which is usually done by applying a layer of aluminium, which may improve reflectivity, or, especially in the case of CZ, by vacuum deposition of diamond, which may temper dispersion.