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A jigsaw puzzle is a tiling puzzle that requires the assembly of numerous small, often oddly shaped, interlocking and tessellating pieces. Each piece usually has a small part of a picture on it; when complete, a jigsaw puzzle produces a complete picture. In some cases more advanced types have appeared on the market, such as spherical jigsaws and puzzles showing Optical Illusions.
Jigsaw puzzles were originally created by painting a picture on a flat, rectangular piece of wood, and then cutting that picture into small pieces with a jigsaw, hence the name. John Spilsbury, a London mapmaker and engraver, is credited with commercialising jigsaw puzzles around 1760. Jigsaw puzzles have since come to be made primarily on cardboard.
Typical images found on jigsaw puzzles include scenes from nature, buildings, and repetitive designs. Castles and mountains are two traditional subjects. However, any kind of picture can be used to make a jigsaw puzzle; some companies offer to turn personal photographs into puzzles. Completed puzzles can also be attached to a backing with adhesive to be used as artwork. Tetris could be considered a virtual jigsaw puzzle.
During recent years a range of jigsaw puzzle accessories including boards, cases, frames and roll-up mats has become available that are designed to assist jigsaw puzzle enthusiasts.
Most modern jigsaw puzzles are made out of cardboard, since they are easier and cheaper to mass produce than the original wooden models. An enlarged photograph or printed reproduction of a painting or other two-dimensional artwork is glued onto the cardboard before cutting. This board is then fed into a press. The press forces a set of hardened steel blades of the desired shape through the board until it is fully cut. This procedure is similar to making shaped cookies with a cookie cutter. The forces involved, however, are tremendously greater and a typical 1000-piece puzzle will require a press which can generate upwards of 700 tons of force to push the knives of the puzzle die through the board. A puzzle die comprises a flat board, often made from plywood, which has slots cut or burned in the same shape as the knives that will be used. These knives are set into the slots and covered in a compressible material, typically foam rubber, the function of which is the ejection of the cut puzzle pieces.
New technology has enabled laser-cutting of wooden jigsaw puzzles, which is a growing segment of the high-end jigsaw puzzle market.
Jigsaw puzzles typically come in 300-piece, 500-piece, 750-piece, and 1,000-piece sizes, however the largest commercial puzzle has 24,000 pieces and spans 428 cm by 157 cm. The most common layout for a thousand-piece puzzle is 38 pieces by 27 pieces, for a total count of 1,026 pieces. The majority of 500-piece puzzles are 27 pieces by 19 pieces. Children's jigsaw puzzles come in a great variety of sizes, rated by the number of pieces. A few puzzles are made double-sided, so that they can be solved from either side. This adds a level of complexity, because it cannot be certain that the correct side of the piece is being viewed and assembled with the other pieces.
There are also three-dimensional jigsaw puzzles. Many of these are made of wood or styrofoam and require the puzzle to be solved in a certain order; some pieces will not fit in if others are already in place. Also common are puzzle boxes: simple three-dimensional jigsaw puzzles with a small drawer or box in the center for storage.
Another type of jigsaw puzzle, which is considered a 3-D puzzle, is a puzzle globe. However like a 2-D puzzle, a globe puzzle is often made of cardboard and the assembled pieces form a single layer. But mainly like a 3-D puzzle, the final form is a three-dimensional shape. Most globe puzzles have designs representing spherical shapes such as the Earth, the Moon, and historical globes of the Earth.
There are also computer versions of jigsaw puzzles, which have the advantages of requiring zero cleanup as well as no risk of losing any pieces. Many computer based jigsaw puzzles do not allow pieces to be rotated, so all pieces are displayed in their correct orientation. These puzzles are thus considerably easier than a physical jigsaw puzzle with the same number of pieces.
Many puzzles are termed "fully interlocking". This means that adjacent pieces are connecting such that if you move one piece horizontally you move all, preserving the connection. Sometimes the connection is tight enough to pick up a solved part holding one piece.
Some fully interlocking puzzles have pieces all of a similar shape, with rounded tabs out on opposite ends, with corresponding blanks cut into the intervening sides to receive the tabs of adjacent pieces. Other fully interlocking puzzles may have tabs and blanks variously arranged on each piece, but they usually have four sides, and the numbers of tabs and blanks thus add up to four. The uniform-shaped fully interlocking puzzles are the most difficult, because the differences in shapes between pieces can be very subtle.
Some puzzles also have pieces with non-interlocking sides that are usually slightly curved in complex curves. These are actually the easiest puzzles to solve, since fewer other pieces are potential candidates for mating.
Most jigsaw puzzles are square, rectangular, or round, with edge pieces that have one side that is either straight or smoothly curved to create this shape, plus four corner pieces if the puzzle is square or rectangular. Some jigsaw puzzles have edge pieces that are cut just like all the rest of the interlocking pieces, with no smooth edge, to make them more challenging. Other puzzles are designed so the shape of the whole puzzle forms a figure, such as an animal. The edge pieces may vary more in these cases.
Since the earliest days of jigsaw puzzles the manufacturers have constantly endeavoured to create new cutting styles that differentiate their work. Even amongst modern, mass-produced puzzles there is considerable variation in the size, shape and intricacy of individual pieces.
The method of cutting pieces varies from puzzle line to puzzle line. Two puzzles of the same size and series from the same manufacturer usually have exactly the same cut, since the cutting dies are complex and expensive to make and so are used repeatedly from puzzle to puzzle. This enables disparate puzzles to be combined in odd ways. Larger puzzles are commonly cut into two or more sections.
More recently, technology such as computer controlled laser and water-jet cutting machines have been used to give a much wider range of interlocking designs in wood and other materials. These methods, however, have the undesirable effect of removing a small amount of material giving a loose fit with the adjoining pieces.
Beginning in the 1930s, jigsaw puzzles were cut using large hydraulic presses which now cost in the hundreds of thousands of dollars. The cuts gave a very snug fit, but the cost limited jigsaw puzzle manufacture only to large corporations. Recent roller press design achieve the same effect, at a lower cost.
The most common approach to building a puzzle is to start by separating the edges from the inside pieces. Once the edges are built it can become easier to move inward. For those new to puzzles, it is recommended to choose one consisting of multiple areas with contrasting designs and colors. This enables the narrowing down of potential portions of the puzzle where a particular piece will fit.
Some people like to use the picture on the box to help solve the puzzle. Once you have completed the edge, if you can find the location of a particular piece on the picture, you can place it down inside of the overall puzzle at approximately the place it belongs. If you do this enough times, you find pieces eventually will start fitting together.
Another approach is to sort the pieces by color, and work on one color at a time. When you get to large areas with the same color (such as the sky in many landscape puzzles), you can go by shape, or you can place all the pieces in a grid and approach the problem by taking a piece that already has an anchor (such as an edge piece) and trying it against all the pieces laid out.
Many large jigsaw puzzles have redundancy in their cut pattern. Many have 180° rotational symmetry around their centre point. Puzzles of 1000 pieces also usually involve a smaller cut pattern that is repeated 4 or 6 times over the whole jigsaw, and that smaller cut pattern usually also has 180° rotational symmetry, so a particular shape may appear 8 or 12 times in the puzzle (although with truncation for edge pieces). It is possible to identify the presence of these symmetries or repetitions relatively early in the process of completing the edge frame. When redundancy is identified, it is possible to use already solved parts of the puzzle to identify the exact shapes of pieces required to complete other sections, greatly simplifying the search.