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Cue balls from (left to right):

• 
  Russian pyramid and kaisa—68 mm (​2 ¹¹⁄₁₆ in)


• 
  Carom—61.5 mm (​2 ⁷⁄₁₆ in)


• International pool—57.15 mm (​2 ¹⁄₄ in)


• 
  British-style pool (large) —56 mm (​2 ³⁄₁₆ in)


• 
  Snooker—52.5 mm (​2 ¹⁄₁₅ in)


• British-style pool (regular)—51 mm (2 in)

Not shown: miniature pool—approximately 38 mm (​1 ¹⁄₂ in).

A billiard ball is a small, hard ball used in cue sports, such as carom billiards, pool, and snooker. The number, type, diameter, color, and pattern of the balls differ depending upon the specific game being played. Various particular ball properties such as hardness, friction coefficient and resilience are important to accuracy.

History

Early balls were made of various materials, including wood and clay (the latter remaining in use well into the 20th century). Although affordable ox-bone balls were in common use in Europe,^[1] elephant ivory was favored since at least 1627 until the early 20th century;^[2]:17 the earliest known written reference to ivory billiard balls is in the 1588 inventory of the Duke of Norfolk.^[3] By the mid-19th century, elephants were being slaughtered for their ivory at an alarming rate, just to keep up with the demand for high-end billiard balls – no more than eight balls could be made from a single elephant's tusks.^{[citation needed]} Dyed and numbered balls appeared around the early 1770s.^[2]:17 The billiard industry realized that the supply of elephants (their primary source of ivory) was endangered, as well as dangerous to obtain (the latter an issue of notable public concern at the turn of the 19th century).^[2]:17 Inventors were challenged to come up with an alternative material that could be manufactured, with a US$10,000 prize being offered by a New York supplier,^[2]:17Phelan and Collender.^{[citation needed]} (This would be worth approximately $188,225.0 in 2019^[4].)

Although not the first artificial substance to be used for the balls (e.g. Sorel cement, invented in 1867, was marketed as an artificial ivory), John Wesley Hyatt invented a composition material in 1869 called nitrocellulose for billiard balls (US patent 50359, the first American patent for billiard balls). It is unclear if the cash prize was ever awarded, and there is no evidence suggesting he did in fact win it.^[2]:17[5] By 1870 it was commercially branded Celluloid, the first industrial plastic. However, the nature of celluloid made it volatile in production, occasionally exploding, which ultimately made this early plastic impractical.^[2]:17 Subsequently, to avoid the problem of celluloid instability, the industry experimented with various other synthetic materials for billiard balls such as Bakelite, Crystallite and other plastic compounds.

The exacting requirements of the billiard ball are met today with balls cast from plastic materials that are strongly resistant to cracking and chipping. Currently Saluc, under the brand names Aramith and Brunswick Centennial, manufactures phenolic resin balls.^[6][7] Other plastics and resins such as polyester (under various trade names) and clear acrylic are also used, by competing companies such as Elephant Balls Ltd.^[8] and Frenzy Sports.^[9]

Ivory balls remained in use in artistic billiards competition until the late 20th century.^[2]:17

Types

Carom billiards

Carom balls, four-ball needs an additional object ball.

In the realm of carom billiards (or carambole) games, three balls are used to play straight-rail, three-cushion, balkline, five-pins, and related games on pocketless billiards tables. The exception is four-ball which needs an extra object ball. Carom balls are not numbered, and at 61–61.5 mm (between approximately ​2 ³⁄₈ and ​2 ⁷⁄₁₆ in) in diameter^[10] are larger than pool balls. The 61.5 mm size are more common. They are typically colored as follows:

• Red object ball (or, uncommonly, blue; two object balls are used in four-ball)


• White cue ball for player 1


• White with a spot (or sometimes yellow) cue ball for player 2

Pool

Old style Brunswick pool balls, the numbers are not located on the stripe

Modern style Super Aramith Pro pool balls racked in Cribbage arrangement

Pool balls are used to play various pool (pocket billiards or pool billiards) games, such as eight-ball, nine-ball and one-pocket. In North America and Asia, they are referred to simply as "billiard balls" (except among carom and snooker players). These balls, used the most widely throughout the world, are considerably smaller than carom billiards balls, slightly larger than British-style pool balls and substantially larger than those for snooker. According to WPA/BCA equipment specifications, the weight may be from 5.5 to 6.0 oz (160–170 g) with a diameter of 2.250 in (57.2 mm), plus or minus 0.005 in (0.127 mm).^[11][12] These are often referred to as 2 ¹⁄₄-inch (57 mm) balls. The balls are numbered and colored as in the table.

Extended set for baseball pocket billiards.

In baseball pocket billiards, the ball set is extended to 21 balls, in which the 16 ball is black and white, while balls 17 through 21 have no special design, but look exactly like balls 9 through 13, respectively, except for their numbers.

Balls 1 through 7 are often referred to as solids and 9 through 15 as stripes though there are many other colloquial terms for each suit of balls (highs and lows, etc.). Striped balls were introduced around 1889.^[2]:246 Though it looks similar to the solids, the 8 ball is not considered a solid because it is the only ball that is black. Some games such as nine-ball do not distinguish between stripes and solids, but rather use the numbering on the balls to determine which object ball must be pocketed. In other games such as three-ball and straight pool neither type of marking is of any consequence. In eight-ball, straight pool, and related games, all sixteen balls are employed. In the games of seven-ball, nine-ball, ten-ball and related, only object balls 1 through 7, 9 and 10, respectively (plus the cue ball) are used.

Some balls used in televised pool games are colored differently in order to make them distinguishable on television monitors. Specifically, the 4 ball is colored pink instead of dark purple, and the 12 is white with a pink stripe, to make it easier to distinguish their color from the black 8 ball, and similarly the 7 and 15 balls use a light tan color instead of a deep brown. Television was also the genesis of the cue ball with six red spots on its surface (known as a "measle" cue ball) so that spin placed on it is evident to viewers.

Coin-operated pool tables such as those found at bars historically have often used either a larger ("mudball") or denser ceramic weighted cue ball, such that its extra weight makes it easy for the cue ball return mechanism to separate it from object balls (which are captured until the game ends and the table is paid again for another game) so that the cue ball can be returned for further play, should it be accidentally potted. In Asia and Europe, some pool tables use a smaller cue ball instead. Modern tables usually employ a magnetic ball of regulation or near-regulation size and weight, since players have complained for many decades that the heavy and often oversized cue balls do not "play" correctly.

British-style pool (blackball)

Setup for blackball

In WPA blackball and its predecessor WEPF or English eight-ball pool (not to be confused with the games of eight-ball or English billiards), fifteen object balls again are used, but fall into two unnumbered groups, the reds (or less commonly blues) and yellows, with a white cue ball, and black 8 ball. Aside from the 8, shots are not called since there is no reliable way to identify particular balls to be pocketed. Because they are unnumbered they are wholly unsuited to certain pool games, such as nine-ball, in which ball order is important. They are noticeably smaller than the American-style balls, and with a cue ball that is slightly smaller than the object balls, while the table's pockets are tighter to compensate. Neither the WPA nor the WEPF (publicly) define ball or even table dimensions, though presumably^{[citation needed]} league and tournament organizers are given some guidelines in this regard. Most manufacturers that supply this market provide sets that range from 2 inches (51 mm) up to 2 ³⁄₁₆ inches (56 mm), often with a slightly smaller cue ball, e.g. 1 ⁷⁄₈ in (48 mm) for a 2-inch set. The most common object ball diameters are 2 in (51 mm) and 2 ¹⁄₈ in (54 mm). The yellow-and-red sets are sometimes commercially referred to as "casino sets" (they were formerly used for televised eight-ball championships,^[2]:45 most often held in casinos). The use of such sets, however, predates television, as they were used for B.B.C. Co. Pool, the forerunner of modern eight-ball, at least as early as 1908.^[2]:24

Snooker

Complete set of snooker balls.

Colour	Value
Red	1 point
Yellow	2 points
Green	3 points
Brown	4 points
Blue	5 points
Pink	6 points
Black	7 points

Ball sets for the sport of snooker look at first glance like a mixture of American- and British-style pool balls. There are twenty-two balls in total, arranged as a rack of 15 unmarked reds, six colour balls placed at various predetermined spots on the table, and a white cue ball. (See snooker for more information on ball setup.)

The colour balls are sometimes numbered American-style, with their point values, for the amateur/home market, as follows in the adjacent table.

Snooker balls are technically standardized at 52.5 mm (2.07 in) in diameter within a tolerance of plus or minus 0.05 mm (0.002 in). No standard weight is defined, but all balls in the set must be the same weight within a tolerance of 3 g (0.11 oz).^[13] However, many sets are actually 2 ¹⁄₁₆ in (52.4 mm), even from major manufacturers. Snooker sets are also available with considerably smaller-than-regulation balls (and even with ten instead of fifteen reds) for play on smaller tables (down to half-size), and are sanctioned for use in some amateur leagues. Sets for American snooker are typically 2 ¹⁄₈ in (54.0 mm), with numbered colour balls.

The set of eight colours used for snooker balls (including white) are thought to be derived from the game of croquet. Snooker was invented in 1884 by British Army officers stationed in India. Croquet reached its peak popularity at the same time, particularly amongst people in the same social context. The eight coloured balls of croquet use the same identical set of eight colours. There are many other similarities between croquet and snooker, which when taken together, suggest that the derivation of the latter owes much to the existence of the former.^[14]

Other games

Russian pyramid ball at a corner pocket. The relative size of the ball and the pocket makes the game very challenging.

Bumper pool ball near a pocket. The bumpers increase the difficulty in potting the ball.

Various other games have their own variants of billiard balls. English billiards balls are like carom balls but are the same size as snooker balls. Russian pyramid uses a set of fifteen numbered but otherwise all-white balls, and a red or yellow cue ball that may be even larger than carom billiards balls at 68 mm (2¹¹⁄₁₆ in) or 72 mm (2⁴⁄₅ in). The related game kaisa has the same pocket and ball dimensions but uses only five balls: one yellow, two red and two cue balls, one for each player.^[15]Bumper pool requires four white and four red object balls, and two special balls, one red with a white spot and the other white with red spot; all are usually ​2 ¹⁄₈ inch (approximately 52.5 mm) in diameter. Bar billiards uses six or seven white balls (depending on regional variations) and one red ball 1 ⁷⁄₈ in (48 mm) in diameter.

Training balls

The Jim Rempe Training Ball

Several brands of practice balls exist, which have systems of spots, stripes, differently colored halves and/or targeting rings.

For example, Saluc markets several practice ball systems, including the Jim Rempe Training Ball, a cue ball marked with rings and targets on the surface of the ball so that the practicing player can better judge the effects of very particular amounts of sidespin, topspin, backspin and other forms of cue ball control, and learn better control of cue stroke.^[16] Various competing products, such as several other Saluc models^[16] and Elephant Practice Balls,^[17] use a similar aiming system. Some such sets consist of just a special cue ball and manual, while others also include an object ball marked for aiming practice.

Novelty balls

Various novelty pocket billiards balls. Clockwise from the top: Red and white balls and markers from a proprietary game called Starball; an Elvis Presley commemorative cue ball from Graceland; a leopard-patterned 9 ball; colorful balls from a poker-themed set; regular balls and the small "jack" from a miniature bocce set used on a table instead of a lawn or court.

There is a market for specialty cue balls and even entire ball sets, featuring sports team logos, cartoon characters, animal pelt patterns, etc.

Entrepreneurial inventors also supply a variety of novelty billiard games with unique rules and balls, some with playing card markings, others with stars and stripes, and yet others in sets of more than thirty balls in several suits. Marbled-looking and glittery materials are also popular for home tables. There are even blacklight sets for playing in near-dark. There are also practical joke cue and 8 balls, with off-center weights in them that make their paths curve and wobble. Miniature sets in various sizes (typically ​ ²⁄₃ or ​ ¹⁄₂ of normal size) are also commonly available, primarily intended for undersized toy tables. Even an egg-shaped ball has been patented^[18] and marketed under such names as Bobble Ball and Tag Ball.

In popular culture

A Magic 8 Ball

Ballistic missile submarine USS Sam Rayburn displays a billiard motif on her missile hatches

The 8 ball is frequently used iconically in Western, especially American, culture. It can often be found as an element of T-shirt designs, album covers and names, tattoos, household goods like paperweights and cigarette lighters, belt buckles, etc. A classic toy is the Magic 8-Ball "oracle". A wrestler, a rapper, and a rock band have all independently adopted the name. The term "8 ball" is also slang both for ​ ¹⁄₈ oz. of cocaine or crystal meth, and for a bottle of Olde English 800 malt liquor. It has also been used to refer to African-Americans, particularly those of darker skin tones, as in the film Full Metal Jacket. The expression "behind the eight [ball]" is used to indicate a dilemma from which it is difficult to extricate oneself. The term derives from the game kelly pool.^{[19][20][21][22][23]} In the Seinfeld episode "The Reverse Peephole", the character Puddy wears a jacket featuring the eight-ball.

Because the collisions between billiard balls are nearly elastic, and the balls roll on a surface that produces low rolling friction, their behavior is often used to illustrate Newton's laws of motion. Idealized, frictionless billiard balls are a staple of mathematical theorems and physics models, and figure in dynamical billiards, scattering theory, Lissajous knots, billiard ball computing and reversible cellular automata, Polchinski's paradox, contact dynamics, collision detection, the illumination problem, atomic ultracooling, quantum mirages and elsewhere in these fields.

"Billiard balls" or "pool balls" is the name given to balls used in stage magic tricks, especially the classic "multiplying billiard balls". Though obviously derived from real billiard balls, today they are usually smaller, for easier manipulation and hiding, but not so small and light that they are difficult to juggle, as the magic and juggling disciplines have often overlapped since their successful combination by pioneers like Paul Vandy.

An urban legend received cultural attention to many saying, "If the Earth were the size of a billiard ball, it would be smoother". It was used in 2008's Discover Magazine,^[24] but mistook the diameter tolerance for smoothness. If the Earth were reduced to the size of a billiard ball, much of it, excluding the Himalayas and Mariana Trench, would be smoother.^[25] (see also: Earth's Shape)

The phrase "as smooth as a billiard ball" is sometimes applied to describe a bald person, and the term "cue ball" is also slang for someone who sports a shaved head.

In Polandball, numbered pool balls are used to denote aboriginal, prehistoric, or native peoples who do not have a flag of their own. Green 6-balls also denote extraterrestrials.

References

Patents

• 
  U.S. Patent 0,050,359—Billiard ball ca. 1865
  


• 
  U.S. Patent 0,076,765—Billiard ball ca. 1868
  


• 
  U.S. Patent 0,088,634—Billiard ball ca. 1869
  


• 
  U.S. Patent 0,114,945—Billiard ball ca. 1871