Although popular with the Egyptians and the Romans, turquoise was not common in the west during the Dark and Middle Ages. It was in the 14th century that it began to be used more frequently, usually for religious jewellery and ornaments. Turquoise began to be used in non-religious jewellery in the 16th, 17th and 18th centuries. It was used in particular in sentimental flower jewellery as the blue colour was similar to the blue forget-me-not flower. In the 19th century, turquoise was also used a lot in Egyptian revival pieces.
Turquoise is one of the most imitated gemstones and has been throughout its use in history. As a result of shortages of turquoise, the Egyptians produced an artificial imitation of turquoise, faience, which was made of glazed earthenware. Another imitant, which began to be used in the Middle Ages, was ‘bone turquoise’ or ‘odontolite’, which is fossilized tusks of mammoths or mastodons. Over a long period, the ivory is replaced by minerals. The material is a greeny blue or a gray blue , but it is believed that Cistercian monks developed a process to heat it to a sky blue. In the early 1800s, odontolite was mined commercially in the southern French Department of Gers.
An article published in the Gems & Gemology journal) described a scientific examination undertaken of six antique brooches from the early to mid 19th century which had been made in France. They were of a similar design, an ornate bow, some with a central diamond. Photos of these brooches had been included in a leading text on antique jewellery as examples of turquoise jewellery. There were a total of 313 blue cabochons in the six brooches and examination found that 288 were made of odonolite, 10 were turquoise and 15 were artificial glass. None of the turquoise stones showed signs of dying, waxing or stabilization which are common treatments today.
Turquoise imitants in later 19th century jewellery, particularly non-French jewellery, were more likely to be glass than odonolite. It is quite hard to identify such imitants although the use of the spectroscope and long wave UV can assist, plus the loupe and microscope. Sometimes, there may only be one or two imitation stones, probably replacing lost or damaged turquoise.
Antique European turquoise jewellery will be set in gold and is often pavé set, that is, small beads or stones set closely together.
Substitutes for modern turquoise are common and are likely to be dyed howlite or magnesite, both naturally a white stone. Howlite also has natural veining similar to the turquoise from Nevada. Pierre Gibson produced a synthetic turquoise in 1972, both as a uniform coloured stone and one with matrix. Natural turquoise today is also likely to have undergone treatments which include waxing, oiling, dyeing and stabilising. This is particularly the case with the distinctive silver set jewellery produced by the Navajo and other Southwestern Native American tribes today. Interestingly, this jewellery is believed to have evolved around the 1880s.
Article: ‘A Historic Turquoise Jewelry Set containing Fossilized Dentine and Glass’ by Krzemnicki, Herzog and Zhou, Gems & Gemology, Winter 2011.