Various materials have been used for Mah Jongg tiles. Some of purely natural materials. Like bone, ivory and bamboo. Especially from the East. But wood, cardboard, stone and even metal too. Mostly for Western sets.
Synthetic materials appear in the twenties. Mainly in America and Europe. Those tiles, skillfully engraved by hand or mechanical means, are made of Bakelite (named after Belgian Leo Hendrik Arthur Baekeland, 1863-1944), celluloid (often with an ivory pattern, the so called French Ivory), Catalin, artificial resins and other kinds of plastics.