hard rubber, vulcanite, ebonite(noun)

a hard nonresilient rubber formed by vulcanizing natural rubber

ebonite(Noun)

The relatively hard product of vulcanizing natural rubber with sulfur; vulcanite

Ebonite(noun)

a hard, black variety of vulcanite. It may be cut and polished, and is used for many small articles, as combs and buttons, and for insulating material in electric apparatus

Ebonite

Hard vulcanized India rubber, black in color. Specific resistance in ohms per cubic centimeter at 46º C. (115º F.): 34E15 (Ayrton); specific inductive capacity, (air = 1): 2.56 (Wüllner); 2.76 (Schiller); 3.15 (Boltzmann). It is used in electrical apparatus for supporting members such as pillars, and is an excellent material for frictional generation of potential. Its black color gives it its name, and is sometimes made a point of distinction from Vulcanite, q. v.