French jet is a trade name for black glass that imitates the appearance of jet, a fossilised wood used in mourning jewellery. The term is a misnomer in two respects: French jet is not jet, and it was not exclusively French. The material and the styles associated with it dominated the production of mourning jewellery in Europe and North America from the 1860s through the early 1900s, and surviving examples remain a substantial category in the antique trade.

The mourning context

The Victorian mourning code, codified through the second half of the nineteenth century and amplified by the example of Queen Victoria's prolonged mourning for Prince Albert from 1861 onward, prescribed a graduated dress for widows, daughters, and other relatives of the deceased. The code distinguished between full mourning (deep mourning, with no jewellery or only black jet), second mourning (with jet, dull black gemstones, or hair jewellery), and half mourning (with grey, lavender, or white). Mourning periods could extend for two and a half years for a widow, with progressively lighter dress permitted as time passed.

The demand for black mourning jewellery was substantial, sustained, and largely middle-class. The principal source of jet itself was Whitby on the North Yorkshire coast of England, where the local jet industry employed approximately 1,500 workers at peak in the 1870s. Whitby jet is fossilised monkey-puzzle wood (Araucaria) from the Lower Jurassic, found as small thin pieces in shale and worked by hand. Production capacity was limited, and the price of fine jet was substantial.

French jet as a substitute

French jet, more accurately described as black glass, was developed as a cheaper substitute for genuine jet. The material was manufactured by glassmakers in France (particularly around Saint-Genis-Laval near Lyon), in Bohemia, and in Birmingham. The black colouration was produced by manganese, cobalt, and iron oxides in the glass batch. Production methods included pressing into moulds, faceting on small lapidary wheels, and stringing of beads.

Visually, French jet differs from genuine Whitby jet in several respects. French jet is denser (specific gravity approximately 2.5 for glass versus 1.3 for jet), feels colder to the touch, takes a higher polish on facets, and is more brittle. French jet rings true under tap; genuine jet sounds dull. Genuine jet warms quickly to the hand and is light; glass remains cool. These distinctions are useful for trade attribution today, when both materials appear in the secondary market in considerable volume.

Style and design

French jet was used for the same forms as genuine jet but, because of its lower cost, in larger and more elaborate constructions than would have been possible in jet. The characteristic French jet pieces include large parures with necklaces, earrings, brooches, and bracelets en suite; long sautoir necklaces of beads or carved drops; and Art Nouveau period brooches with naturalistic decoration. The faceted construction, often with claw-set faceted glass on rolled metal frames, is particularly characteristic of French jet pieces produced from the 1880s onward.

The metal mounts for French jet pieces are typically gilt brass, blackened iron, or low-carat gold. The Berlin iron jewellery tradition of the early nineteenth century, in which fine cast iron was given to the state in exchange for gold during the Napoleonic Wars and re-emerged as a prestige material, has stylistic links to French jet through the use of black metal as an aesthetic vocabulary. Gutta-percha (a natural rubber from Palaquium trees), bog oak, vulcanite (vulcanised rubber), and onyx were all used in similar mourning roles. Jet, French jet, gutta-percha, and vulcanite are commonly confused in catalogue descriptions and require careful examination to distinguish.

Decline and afterlife

The decline of mourning jewellery as a category, accelerating from the death of Queen Victoria in 1901 and effectively complete by the First World War, ended the market for French jet as a contemporary product. The post-war social code rejected prolonged mourning, and the dress conventions that had sustained the market dissolved. The Whitby jet industry collapsed quickly; by 1936 only fewer than ten workers remained in the trade. French jet production transitioned in part to other black-glass applications including evening wear, where it persisted through the Art Deco period.

In the contemporary antique trade, French jet pieces are common, generally affordable, and increasingly collected. Large fully-fitted parures in original cases are the most desirable category. Faceted French jet beads remain a staple of vintage costume restringing, although the brittleness of the material and the small size of typical drilled holes make handling demanding. Misattribution as jet is widespread in the lower end of the trade, and trade ethics require that the distinction be drawn correctly when the material is identified.

Trade considerations

For dealers and appraisers, the distinction between Whitby jet and French jet is material to value. A genuine Whitby jet parure of comparable visual elegance to a French jet parure may be priced two to five times higher in the current market. Identification by hand-feel and weight is reliable for experienced dealers; specific gravity testing settles ambiguous cases. The hot point test, in which a heated needle is briefly applied to an inconspicuous part of the piece, distinguishes jet (which produces a coal-like odour) from glass (which is unaffected) and from gutta-percha or vulcanite (which produce characteristic burning rubber odours). The hot point test is destructive at the point of application and is not used on intact decorative surfaces.