What are billiard balls made of?

In the past, many balls were made of ivory; since the animals that produced this have become endangered species, other materials, such as wood and various plastics have been used.

In 1865, John Wesley Hyatt patented a composition material resembling ivory (Celluloid) for a billiard ball (US50359), winning $10,000 prize from Phelan and Collender of New York City for the best substitute for ivory. This was the first U.S. patent for billiard balls. Unfortunately, the nature of celluloid gave these billiard balls a tendency to occasionally explode, adding additional spark to the game but ultimately making this first plastic impractical for such use.

Modern billiard balls are most often made from phenolic resin.

Billiard balls are made up of man-made resins, commonly phenolic and polyester. The resin, in liquid form, is poured or injected in moulds. The moulds are broken and the balls are polished and painted.

MARBLE OR ENAMEL???