NNP

Hard Rubber.  A firm, inelastic, nonmetallic composition once used for medallic items, not replaced by plastics. The hard rubber is formed from natural rubber (terpene hydrocarbon) treated with sulfur – the harder the rubber the greater the amount of sulfur present during the initial heating. When left in natural state hard rubber is blank (called ebonite); it can also be artificially colored by dyes (called vulcanite, from the vulcanized process).  See illustration, product medal.

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators

COMPILED AND WRITTEN BY D. WAYNE JOHNSON

Roger W. Burdette, Editor