Dominoes are flat, rectangular, and marked with an arrangement of dots or “pips” that resemble those on dice. The domino set also has a blank side that may be inscribed with an identifying mark or left blank. The number of pips on each domino face usually determines what game can be played with it. There are many different games to be played with a set of dominoes, and each has its own rules and scoring system.
Most dominoes are made of polymer, which is cheaper and durable than other materials. But there are also sets made of other natural substances, such as bone, silver lip ocean pearl oyster shell (mother of pearl), ivory, and dark hardwoods like ebony; ceramic clay; metals, such as brass or pewter; and even crystal. Such sets are generally more expensive and have a more elegant appearance.
Some dominoes have a metal pin, or spinner, in the center that is used to hold another domino in place while allowing it to be moved along a line of play. When a double domino is used in this way, the number of dots on each open end is cut off for scoring purposes; only the total score for the entire line of play is counted.
The number of dominoes a player has in his or her hand at the end of the round is the winner’s score. In teams, the winning team scores based on the number of multiples of five in its opponents’ hands.
When all the dominoes are set up on a table, a player can begin playing by putting down one bone or square of domino. This is called “setting” or “putting down” the first bone of a hand and is done in turn by each player.
If a domino has no open ends, it is said to be “sleeping.” Players cannot put down a sleeper during their turn unless there are already dominoes on the table that they can use to make a line of play. This is a rule to prevent dominoes from becoming too crowded and creating an unfavorable score for the next player.
Dominoes are sometimes used as parts of Rube Goldberg machines, and there are even competitive domino shows in which builders attempt to create complex effects or reactions using a series of dominoes set up in careful sequence. As with the set of chess pieces, dominoes have inertia and resist motion when there is no outside force pushing on them. But a single small nudge can cause the whole row to fall over. This is why dominoes are so popular to play. They are fun to set up, and they can tell a story or inspire the imagination.