A small rectangular block of wood or plastic, a domino has a double-edged surface and is marked with an arrangement of spots, or pips, like those on a die. The dominant side bears a value, which can range from six to none. The other side is either blank or identically patterned. In positional games, one domino is positioned edge to edge with another, with the two matching ends touching fully. The resulting chain is known as the line of play, and may extend lengthwise or across it. Each new tile placed adjacent to the line of play must be either a single or a double.
When a domino is pushed onto the line of play, it transfers potential energy to the other pieces that make up the chain. This energy can then be tapped to move the next domino along the line, or it can continue flowing through the chain until the final piece falls. Domino chains can be as simple or complex as the players want, with straight lines and curved ones, grids that form pictures when they are arranged, or even 3D structures such as towers or pyramids.
In most domino variants, the goal is to score points by attaching a domino from one’s hand to the ends of the tiles already in the line of play. A point is scored whenever the sum of the end tiles is divisible by five or three. The winning player usually scores the most points.
Traditionally, domino sets have been made from a variety of natural materials, including bone, silver lip ocean pearl oyster shell (mother-of-pearl), ivory, or ebony, with contrasting black or white pips. More recently, domino sets have been produced in a variety of polymer-based materials. Although some players prefer to use natural-material sets, these are often more expensive than the plastic-based alternatives.
Players begin a game of domino by drawing the number of tiles allowed by the rules of the particular game they are playing. The player with the heaviest double then plays a tile, beginning the domino chain with whichever of its ends has the lowest value. The next players must then place their tiles, positioning them in such a way that they touch at least one of the ends of the domino chain, which continues to grow in size.
When the domino chain is complete, one player may choose to “buy” additional tiles from the stock, if permitted by the rules of that game. However, it is also possible for players to buy each other’s tiles, a process known as passing and byeing.
After each player has drawn the number of tiles he or she is allowed to take, a domino chain begins to develop on the table. The first domino to be played must be a double, since only those tiles have matching ends. After a double is played, the next domino to be added to the chain must be either a single or a pair of adjacent doubles. In most domino games, the doubles must be played crosswise; singles may be played lengthwise.