Vulcanite is compressed (vulcanized)rubber. Vulcanite was a less expensive material than jet and used for similar jewelry items. Vulcanite is sometimes erroneously called gutta percha which is actually a substance from the Malayan palaquium tree of which very little survived.

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Victorian Era Carved Vulcanite Pin in the Form of a Delicate Hand with Lace Cuff Holding a Perfect Rose.
Photo Courtesy of Lang Antiques.