Opals are the second gemstone for October. Precious opal displays a play of colour against a white, translucent or dark background. It is the background that describes and defines the type of opal. Black opals, the national gemstone of Australia, has a black, brown or dark gray background, white opal has a white or cream background and crystal opal is translucent. The play of colour is a display of iridescent colours – blue, green, yellow and/or red – which change depending on the direction you hold the gemstone.
There are other types of opal like boulder and the matrix opals in which the opal is either an inseparable surface layer on top of the underlying rock or is embedded as a part of the rock itself. Then there is the fire opal from Mexico, usually an orange, red or yellow colour, and a precious fire opal from Ethiopia which can also display a play of colour.
In antique jewellery, the most common precious opals found are white or crystal opals as black opals from Australia were not commercially mined until 1903. The opals were mined in Czernewitsa in Hungary, in what is now Slovakia. Popular with the Romans and for a number a centuries following, opals became associated with bad luck from the late 17th century until the middle to late 19th century. They became popular again with the rise of Art Nouveau and Belle Epoque jewellery as the delicate colours of opals suited the new styles of jewellery perfectly..
Opals are quite soft and can crack easily so are best suited for earrings, pendants and brooches but we do see them used in rings and bracelets so care needs to be taken with them. They are usually cut as cabochons.
It is important to be aware that so much opal jewellery sold today is either an opal doublet or opal triplet and it is often difficult to tell this. Opals can be quite thin and so the opal doublet was created to enable this thin slices of (normally) black opal to be used in jewellery. With a doublet, a slice of opal is cemented onto a dark base or a transparent material. An opal triplet is a composite consisting of three pieces – usually a transparent or translucent thin slice or lamination of natural opal which is cemented to a dark base material, with a top layer of clear material cemented over the top. It can be very hard to identify doublets set in jewellery. Generally, if the back of an opal set in jewellery is closed, then it is likely to be a doublet or triplet. The important point is that the seller of the opal must disclose to the buyer that the opal is a doublet or triplet and is not a solid opal.