Dominoes are small rectangular blocks of wood or plastic marked with dots resembling those on dice. They are normally twice as long as they are wide and may feature a line in the middle that divides them visually into two squares, each with a value indicated by the number of spots or pips on either end (normally from six to zero). The value of a domino is also sometimes called its rank or weight.
Many different games are played with dominoes. The most common are blocking and scoring games, but there are also games that involve a more complicated interaction between players or between player and machine. Some of these games are variations on card and dice games, while others have been developed to circumvent religious proscriptions against playing cards.
Most of the domino games that are played can be classified into four categories: bidding, blocking, scoring, and round. These games usually feature a line of dominoes that increases in length as each player plays a tile. The line of play is sometimes called the string or layout. Each tile must be matched to the open end of one of the previous dominoes in the chain, and then positioned on the table so that it shows only a single domino number.
Depending on the rules of the game, dominoes can be joined to the line of play in one of two ways: 1) across the line of play, crosswise; or 2) with the line of play, lengthwise. Doubles are always played crosswise; singles are generally not.
After the stock of unused dominoes has been shuffled, the first player draws a hand of tiles. He or she then makes the first play according to the rules of the game being played. If the players draw identical hands, a tie is broken by drawing new dominoes from the stock until one hand has more than the other.
Once a player has made a play, the next domino must be laid perpendicular to the current line of play. If the next domino has a matching number to one of the ends of the previous tile, it is joined to that end and the domino chain continues to grow in length. In some cases, a new domino is added to the end of the chain so that it has a matching number at both ends, creating a double-ended domino.
If a player cannot make a play, the hand is “blocked,” and no further plays are possible. The winning player then scores the total number of pips on the exposed ends of the tiles in his or her hand. Some games allow only scores that are divisible by five; others do not have any restrictions on the number of points scored.
The majority of domino sets are made from polymer materials, but there are also some sets that have been manufactured in other natural materials such as bone, silver lip ocean pearl oyster shell (mother of pearl), ivory, or ebony, which are often characterized by a richer feel and a more substantial weight. Many domino set designers create sets in a variety of interesting forms and shapes, including curved lines, grids that form pictures when the dominoes fall, or 3D structures such as towers and pyramids.