I have talked about various ways in which antique gemstones might have been treated and enhanced to look better. Foiling was a common way to enhance colour in gemstones and many stones were dyed to make them look darker. However, there were also deliberate attempts to make a stone look like another stone. Fake, costume, imitation – whatever you call them, they’re are not exactly what they are purporting to be and they have always been a part of our culture. The use of these imitations has been to deceive us into thinking we have bought the real gem.
Many of the writings about gemstones throughout history discussed recipes for improving gemstones but also discussed imitating them. For instance, the Egyptian Stockholm Papyrus, dated around 400AD, apart from recipes for improving pearls and emeralds, devoted itself with making one stone look like another, that is, the focus is more on substitution and not on enhancement.
The Textbook of Mineralogy by Georgius Agricola in 1556 also discussed the use of quartz and glass to represent sapphires. Skip ahead to 1658, when Natural Magic was published in London by John Baptista Porta and it discusses the making of coloured glass imitations and various treatments such as dyeing sapphires, amethysts, topaz, chrysolite and emeralds, to turn one stone into a more valuable one. In 1760, Don Bernado Monton published Secretos. It contained instructions on how to dye garnets to look like rubies.
Fake pearls, created from glass or polished shells, then coated with a varnish made from ground fish scales, were common in Elizabethan times, particularly for sewing onto clothing but also for jewellery.
A common process for imitating gems in antique jewellery was the creation of doublets, that is, composite stones. Generally, a slice of a real gemstone, say, an almandine garnet, was glued via onto a piece of red glass, placed into a furnace to meld, and then faceted. It was the colour of the glass that determined what gem was been imitated, so while the slice of real gem was usually almandine garnet, different coloured glass was used, depending on what stone was being imitated. Sometimes two smaller pieces of the same gemstones, such as a diamond, were glued together to make it look that the stone was a good size.
Pliny wrote about composite sardonyx stones, created by gluing together a black, a white and a red onyx slices of stones, to be used for intaglios or cameos.
Garnet topped doublets were first written about in a book published in 1869 and it is believed that the process was invented by a lapidary in 1845 in Paris. Garnet was used as it fused easily to glass, more so than other gems. Another doublet is the Soude emerald which comprise two pieces of rock crystal cemented together with green dyed gelatine. These were common in the late 19th century. The commercial production of synthetic gems means that the rock crystal or glass has now been replaced by synthetic gems.
The case of composite opals is a little different. The creation of doublets and triplets arose out of the need to use thin pieces of opal rather than to deceive. Opal composite stones are one composite stone that has remained popular into the 20th century. It was not until 1946 that opal doublets in Australia really took off, and triplets became common in the 1960s. Opal doublets are made by placing a thin slice of opal which shows flashes of colour onto a backing of potch, black onyx or black glass. the pieces are cemented together. A triplet is a doublet covered by a cabochon shaped piece of rock crystal or glass. Sellers are supposed to state when an opal is a doublet or a triplet so as not to mislead a buyer into thinking they are buying a solid opal rather than a composite but this is often not the case. The price for a solid opal is a lot higher than the price for a doublet opal.
So in antique jewellery, gems that might be fakes include garnet topped doublets, soude emeralds, opal doublets and triplets, glass pearls, paste stones and foiled stones. It is important to note that not all of the latter two in particular were intended to deceive but, at some time, their production and use was considered acceptable.