Jet—fossilized driftwood similar to coal— is hard, black or dark brown in color, and found primarily in Yorkshire, England, Spain, France's Aude region, Germany, and other parts of northern Europe, Asia, and North America. Often referred to as "Whitby jet," many souvenir and mourning pieces made of this substance were carved and sold in this English town during the peak of its popularity.
History of Jet
Early on, jet was used by the ancient Romans to craft elaborate jewelry and by Native Americans for the ornamentation of weapons. In the 19th century, its use flourished in Europe as one of the few substances appropriate for mourning jewelry. (It was worn outside of mourning too.) Its use declined after 1875, replaced by cheaper options like black onyx (chalcedony), black tourmaline, black glass ("French jet"), and vulcanite.
Around the turn of the 20th century, dwindling supplies of quality material, preferences for more delicate pieces (jet jewelry tends to look massive), and less rigid mourning-dress practices contributed to a loss of interest in the jet material.
Uses of Jet
The pliable nature of jet allows it to be carved, faceted, and polished to a soft warm sheen. Jet jewelry intended for first mourning (the months just after a loved one's passing) was polished to a matte black finish. However, most pieces found today have a polished, glossier appearance.
Jet was used to craft beads and other necklace components which were then strung or linked together with wire. Brooches that display intricate carvings were also constructed with this stone, as were earrings, pendants, and finely crafted jewelry sets.
Today, jet jewelry is coveted by Victorian period collectors and can be found in antique shops, online, and sometimes at flea markets. Authentic jet is opaque black in appearance and void of mold lines, like plastic replications set in a mold. The traditional material was hand carved, so no two pieces will be identical. Most jet jewelry found today is highly polished, but if you're lucky enough to find a piece made for first mourning, it will be matte black.
Natural jet is very light in weight in comparison to French jet, its glass counterpart. Upon the touch, the authentic material takes on a room temperature rather than a cold feel like glass. Additionally, jet will not scratch glass, yet glass will, indeed, scratch jet.
When touched by a hot pin (carefully, and in an inconspicuous location to avoid damaging the jewelry), jet produces a coal-like odor. For a less-risky method of testing, scrape an inconspicuous area of the piece in question onto a rough surface, like the back of a ceramic tile or the bottom of a piece of unglazed porcelain. If it leaves a brown mark, the piece is likely jet. Do note, however, that vulcanite can also leave a brown mark. So, be sure to look for other jet attributes before making the call.
Note: The hot pin test should only be conducted by a professional. A novice collector could ruin an authentic jet piece or cause a fire if the jewelry is made of a celluloid plastic instead.