An example of such a puzzle set is known. The known puzzle is a jigsaw puzzle. The front side of the puzzle pieces comprises a section of an image that is to be completed.

Symbols are printed on the back of each piece to allow the puzzle to be assembled more easily and faster.

A person assembling the known puzzle must take care that all the pieces that are to be placed are lying front side up. Otherwise, this person would inadvertently notice the code.

It is an object of the present invention to provide a puzzle set of the type mentioned above, which comprises a mechanism to only provide a clue to a person assembling the puzzle when it is wanted.

This object is achieved by the puzzle set according to the invention, which is characterised in that the code is disguised in the marking in such a way as to become recognisable when a definite operation is performed.

Because the code is disguised in the marking, the marking need not be kept out of sight. The clue is not readily apparent from looking at the side of the puzzle element to which the marking has been applied. Because the code becomes recognisable when a definite operation is performed, the user can make a conscious decision to obtain a clue relating to the position of the puzzle element.

In a preferred embodiment, the code is disguised in the marking in such a way as to require the use of a viewing instrument to become recognisable.

Thus, in this embodiment, the user must make a conscious decision to operate the viewing instrument in order to obtain a clue.

In another preferred embodiment, the elements with a marking comprise a substance of which the optical properties depend on environmental conditions to which it is subjected.

This has the advantage that no extra article need be provided with the puzzle set, making it cheaper to manufacture.

The user can create the required environmental conditions at home, whenever a clue is desired.

Preferably, the optical properties of the substance are reversibly changeable.

Thus, the puzzle set can be used again, without the clues then being recognisable upon first glance.

In a preferred embodiment, the optical properties change upon irradiation.

Thus, by subjecting the marking on the puzzle element to radiation, for example heat or light, the code will be rendered recognisable. This has the advantage that the rest of the puzzle element remains relatively unaffected.

The invention will now be explained in further detail with reference to the accompanying drawings.

Fig. 1 is a schematic drawing of an assembled jigsaw puzzle.

Fig. 2 is a schematic drawing of a puzzle piece of the puzzle of Fig. 1, with a marking comprising a disguised code on the reverse side.

Fig. 3 is a schematic drawing of the puzzle piece of Fig. 2, showing only the marking.

Fig. 4 is a schematic drawing of the piece of Fig. 2 and of a viewing instrument.

In Fig. 1 an assembled two-dimensional jigsaw puzzle 1 is shown. The jigsaw puzzle comprises puzzle pieces 2, which have been placed in positions to form an assembly. In this example, the puzzle pieces 2 are placed at positions in a matrix, so that their positions can be denoted by a letter identifying a column. and a number identifying the row in which they have been placed.

The invention is not limited to a jigsaw puzzle such as the one shown in Fig. 1. Rather, it relates more generally to any puzzle set comprising a plurality of elements, each to be placed at a certain position in an assembly. The pieces can be interlocking, but they could also. have shapes that allow any piece to be laid next to any other piece. However, each piece must be intended for placement at a certain position, the assembly of correctly placed puzzle elements having some significance to an observer. Preferably, the pieces comprise a face with part of a picture on it, such that the complete picture becomes apparent when all the puzzle elements have been correctly placed at their intended positions. However, this is not a necessary feature of the puzzle set according to the invention. The assembly could also have some sort of shape that has significance to the observer. Significance can merely mean that the appearance is the same as that of a set example.

Although the jigsaw puzzle 1 is two-dimensional, i. e. each piece 2 is to be placed at a position in a plane, the invention also encompasses three-dimensional puzzles, wherein the assembly of correctly placed puzzle elements extends in all three dimensions. The puzzle elements may be made of cardboard, paper, wood, plastics, or any other suitable material.

At least some of the puzzle pieces 2 comprise a marking, which marking contains a code relating to the position of the puzzle element in the assembly. The marking is an element applied to or just below the surface of the puzzle element. Various examples of markings will be given below.

Depending on the type of marking and puzzle, the marking can be on a face of the puzzle element that is not visible in the finished assembly, or it can be on the visible side.

According to the invention, the marking contains a code relating to the position of the puzzle element in the assembly, but the code is disguised in the marking in such a way as to become recognisable when a definite operation is performed. In other words, the marking comprises an arrangement of elements that encode the information allowing the code to be derived, but this information is obscured. A definite operation, i. e. a well-defined series of acts, performed within certain limits, is needed to render the information recognisable, i. e. intelligible to the human observer.

Referring to the example of the jigsaw puzzle, the person laying the puzzle will normally refer to the pieces of the complete picture that are printed on each puzzle piece 2, to determine where to place each piece 2. If the jigsaw puzzle 1 comprises very many pieces 2, comprises a very complex image, or if it is being assembled by a younger user or someone with little time, the information comprised in the picture piece might not be enough. A user wishing some help in laying the jigsaw puzzle may, according to the invention, perform the definite operation required to make the code in the marking on the piece 2 comprehensible, in order to obtain a clue. Thus, enjoyment of the puzzle is increased. The invention has the advantage of providing the user with the option of obtaining a clue. The clue is invisible when the line of sight of a user is at an acute angle to a line perpendicular to the surface on or under which the marking has been applied. Thus, the user need not, for example, take care to keep the pieces 2 that are still to be placed in position face up, as would be the case if the code were to be visible printed on the back of each of the pieces 2.

Many different types of codes are possible within the scope of the invention. In the example of Fig. 1, the code would be a co-ordinate on a two dimensional grid, e. g. Al'for the top leftmost piece. In an alternative embodiment, the code may be a number in a continuous range. The number at the lower boundary of the range may, for instance correspond to the top leftmost corner and the number at the upper limit of the range to the bottom right hand corner. In another embodiment, the code may be a word in a sentence running from left to right and from top to bottom. In yet another embodiment, the code may be a colour or a pattern, corresponding to a section of the plane in which the jigsaw puzzle 1 is to be assembled. In this case, subsets of puzzle elements may be provided with the same code.

Preferably, however, the code contained in each marking is unique to the element comprising the marking. Thus, the maximum in possible help is available to the user.

In one embodiment, a hologram is provided on a side of the puzzle element, or inside a translucent element. It may be provided at a position in or on the element from which it is invisible when assembly of the puzzle has been completed. The definite operation required to make the code recognisable is to turn the puzzle element until it is at the correct angle for revealing the code.

Other embodiments of the puzzle set according to the invention comprise one or more pieces with markings that disguise the codes in such a way that a viewing instrument is required to render the code recognisable. In one embodiment of the invention, a bar code is printed on the reverse side of a two-dimensional jigsaw puzzle piece. A bar code reader is comprised in the puzzle set. When the user wishes to see the code, the bar code reader is used to provide a recognisable code on a display.

In another embodiment the marking comprises a code that is printed on the reverse side of a puzzle piece in such a way as to be invisible, or at least illegible, to a human observer. A viewing implement is required to render the printed code discernible. The code may, for example be printed in very fine print, or the characters may be distorted. In one embodiment, a jigsaw puzzle piece has a very fine code printed on it. When a looking glass comprising a lens is held between the puzzle piece and the eye of the user, the printed code becomes recognisable. It is noted that the code may also be printed in distorted fashion, with the lens being appropriately shaped to compensate for the distortion. It is noted that these embodiments have the advantage that the code can be printed on a side of the puzzle piece that is visible when the puzzle has been assembled, without disturbing the aesthetic impression.

In another favourable embodiment, shown in Figs. 2-4, a code 3 (Fig. 3) is printed on one side of a puzzle element 4. The code 3 is concealed by a layer comprising a pattern of elements 5 (Fig. 2) printed in coloured ink, which normally hide the code.

In this embodiment, a viewing instrument 6 (Fig. 4), comprising an optical element, a lens 7 of transparent glass or plastic, in substantially the same colour as the coloured ink of the elements 5 is provided with the puzzle set. When viewed through the viewing instrument, the colour of the covering layer of elements 5 is filtered out and the printed code 3 underneath is thus revealed.

In yet a further embodiment, a polarising filter is provided with the puzzle set to make the code visible. The code can be disguised in the marking, by providing a marking with a reflective material covered by a transparent light scattering material, wherein the code is printed in the marking by selectively removing the light scattering material. Various alternative embodiments employing a polarising filter are possible.

A number of alternative embodiments of the invention have the advantage that no extra viewing implement is required to render the code recognisable. Instead, these embodiments merely require that the puzzle element or only the marking be subjected to certain environmental conditions. This can also mean that some operation is performed on the marking.

An example of the latter is where the marking comprises a printed code covered by a layer of material that can be scratched away to reveal the code. Such markings are well known from e. g. lottery scratch cards.

Preferably, however, the disguise of the code is reversible. In one embodiment, the marking according to the invention comprises a substance of which the optical properties are changeable, preferably reversibly, by subjection to certain environmental conditions. The term optical properties encompasses the colour, reflectivity, transmittance and light scattering properties.

In one variant, the code itself is printed with an ink comprising such a substance. Such inks are commonly known as invisible inks, and are well known per se. In another variant, the code is printed in stable ink, but covered by such a substance, the substance becoming transparent when subjected to certain environmental conditions.

In one embodiment, the optical properties of the substance vary according to the temperature. The substance has one appearance at ambient temperatures and another at appreciably (at least 5 degrees centigrade, but preferably 10 degrees centigrade or more) different temperatures. In one embodiment, the code is revealed when the element is subjected to appreciably lower temperatures, for example by placing the puzzle element in a refrigerator. In another embodiment, the code is revealed when the marking is heated, e. g. by warming by the hands of a user, or by placing the puzzle element on a radiator, or in the sun.

In a further embodiment of the invention, the properties of the substance depend on the type of radiation.

These substances are also known as photochromic inks. The ink changes colour in response to radiation of a certain wavelength, e. g. ultra-violet radiation.

In another embodiment, the mark comprises a printed code, covered by a substance that is normally opaque, but becomes transparent when brought into contact with water. An example of a technique for producing such markings is disclosed in US-B1-6 364 993.

In yet another embodiment, a sequence of symbols is printed on a side of the puzzle element that is not visible when each element is at its position in the assembly. The sequence of symbols is a ciphered form of the code. The puzzle set further comprises a table relating each sequence of symbols to a corresponding code. The table is thus instrumental to rendering the code recognisable, providing information to decipher the ciphered code.

The invention is not limited to the described embodiments, which can be varied within the scope of the attached claims. For instance, the puzzle elements can be construction elements for a three-dimensional structure.