Answer: ebonites

AnswerCrossword Clue
EBONITESHard black rubbers.
EBONITESVulcanites.
EBONITESHard rubbers
eboniteshard, readily cut and polished rubber, obtained by vulcanizing rubber with a large amount of sulfur, used in the manufacture of combs, buttons, and for electric insulation
ebonitesEBONITE, a hard rubber