Vulcanite and ebonite

Hard rubber, not a gemstone

Vulcanite is a hard material made by vulcanising rubber with sulphur. Ebonite denotes hard rubber, often black, and the names are closely associated in descriptions of older objects. It is not jet, although it was used to imitate jet in brooches, bracelets and necklaces.

Features and possible confusions

Gem-A describes how black vulcanite can develop a brownish or khaki surface after exposure to light. Moulded ornament and attachment methods can provide clues, but colour alone does not confirm the material. Ebonite can also be confused with Bakelite, which is a different material.

A piece of jewellery may contain several materials. Science Museum Group holds a jet brooch with a vulcanite ring that the museum considers a probable replacement. An apparently uniform black object should therefore be examined component by component.

Care and documentation

Old hard rubber may be brittle. The Canadian Conservation Institute describes how deteriorating ebonite can develop acidic surfaces and release substances harmful to other objects. Avoid strong light, heat and damp storage. Separate unstable or odorous components from sensitive materials and seek a conservator's advice.

Do not polish away discolouration or apply solvents and water-based cleaners indiscriminately. Document cracks, colour differences and previous repairs. Browse our jewellery.

Sources

Gem-A on vulcanite, Canadian Conservation Institute on rubber and plastics, the Institute's detailed conservation guidelines and Science Museum Group brooch 2002-309.