Tortoiseshell Glass: from
the Glass Encyclopedia

Tortoiseshell art glass is hand-blown glass in which two layers of blown glass have pieces of brown glass trapped between them. The brown glass is usually in two colors, light and dark brown, and shaped in blotches to resemble the marking on a tortoise, as in the vase shown left.

The original patent for this glass was registered in London by Francis Pohl and S. A. Wittman in 1880 (October 25th). They were from Europe and tortoiseshell glass was made in Germany in the 1880s. Their patent described the process of first blowing bulbs of brown glass and breaking them into fragments onto a hot marver (usually a heated steel or iron plate); then blowing two bulbs of clear glass, one of which was rolled over the brown fragments so that they stuck to the outside of the molten gather of glass. The other bulb of molten glass then had its top cut away so that the bulb with brown pieces could be inserted and the two bulbs joined and blown as one to the required shape. The final product was then coated to produce a yellow stain before firing and annealing (allowing to cool slowly).

This very complicated process produced a beautiful type of art glass, and as usual with 19th century inventions, others invented simpler processes or copied the original. The yellow staining, for example, was not needed if one of the glass bulbs was a pale honey gold colour. There are reports of tortoishell glass being reproduced in Italy recently, but the products were described as being very thick and clumsy.

Tortoiseshell art glass was made in Europe and also in the USA at the Boston and Sandwich Glass Co. in Massachusetts, from 1880 to about 1900. It is generally agreed that distinguishing which factory made a particular item is impossible unless there is a label or makers mark, and these are not usually present on Tortoiseshell glass.