Plastics, synthetic materials by an other name, have been used for many decennia, for the production of mainly cheap Mah Jongg sets. In countries like China, Japan and South Korea tiles are made of a white or ivory colored, hard and stony kind of plastic. The engraving has been molded. The back is made of bamboo or colored plastic.
Personally I dislike these ugly sets intensely. For completeness sake I do however have some in my collection: see the section Modern.
Most of the sets in the section Synthetic, come from East Asia. They were made before and after the Japanese occupation. Meant mainly for Western expats. That is why Western letters and numbers are often added.
The older sets are frequently leather boxes or valises. Brought back to Europe by returnees from the British and Dutch Indies. The sets from after 1945 are mainly meant for tourists.
A few sets in the collection are Western. One, with a later added multiplex box (originally by English toy maker Gibson), has beautiful, white Bakelite tiles of most likely East European origin. Another is American and has black-brown Bakelite tiles wit inlaid illustrations. And the third one is a typical standard set from America. With Catalin tiles in a so called ‘trumpet case’.