The Magic and Science of Opals
Opals have been regarded as talismans of good luck for centuries, and across civilizations they have been imbued with connotations of magical properties. It is understandable that before modern science was able to explain the wonders of the opal stone, people were mystified with the appearance of the opal to the point where they believed it to be otherworldly.
Opals are mineraloids that are formed from hardened silica gel – yes the very same stuff you find at the bottom of a new handbag! – and because they can contain anywhere between 20% and 2% of water, they are not crystalline, unlike most gemstones. This is also the reason that opals are delicate in comparison to other gemstones, in that they can be effected by the environment they are kept in. If they are kept in heat, the moisture that is naturally tapped inside could be dried out, and this causes opals to split and fracture.
The opal’s iridescence is due to the way which the stone is formed. It is the difference in size that occurs between the silica spheres, and the stacks they arrange themselves into during formation, which create the spectrum of colours that we can see. Light refracting from these molecules arranged in different levels causes the refracting in light that the opal is famed and adored for.
These refractions have the effect of displaying colours across the light spectrum to our eyes. The larger the spheres of silica in the opal, the greater the range of the colour spectrum that will be displayed by the opal. This phenomena is exclusive to opals and is known as the ‘play of colour’, which is the variation and abundance of colour that the human eye can detect looking into an opal.
Types of Opals
There are many types of opal, and the type is often determined by where the opal is discovered. Generally speaking, the dark and black opals are the most sought after, and these are usually found in the mines around Lightning Ridge in New South Wales. The most commonly found opals – and the opals that are most frequently found in vintage and antique opal jewellery – are the lighter opals or white opals. Fire opals can be found in Mexico, and these are bright or deep orange; yet have none of the luminosity, lustre or opalescent play of colour that is traditionally associated with this stone.
Other forms of opal – which are more concerned with the formation of the opal rather than the colour – are the boulder opal and matrix opal. Both of these types of opal are attached to or formed within rock or ironstone, which can create a very striking visual effect, either due to the ironstone providing a darker background as a contrast to the opals infamous play of colour, or – as with matrix opals – flashes of the opal appear in veins of colour from behind the ironstone.
The third category of opal and distinction between types of opal is the doublet and triplet opal. Rather than being a naturally occuring type of opal, this type of opal is distinguished by the way which the opal has been cut and prepared for being on display or becoming a gemstone in jewellery. Opal doublets and opal triplets are types of opal which have been backed by a dark background setting – this gives the same impression as the naturally occurring dark or black opals, and is of higher value than an opal triplet, as an opal doublet uses a larger weight of opal than an opal triplet. However, the lack of the resin or protective layer over this large opal means this type of setting is more suceptible to breakage, drying and cracking.
Triplet opals feature the same dark background as doublet opals, yet also have a resilient protective layer over the opal itself. This type of opal is perfect for those who admire the stone yet are cautious of it’s durability. Opal doublets and triplets are often larger opals, used in necklaces and dramatic, larger items of jewellery.
Looking After Your Opals
Opals are more demanding than most stones- they need to be stored out of direct sunlight, and should not be exposed to soaps or perfume; chemicals in general are not the friend of opals. However, for all the opal requires more care and attention than other stones, they also can provide a lifetime of joy and pleasure if cared for correctly.
Furthermore, opals are not as hard wearing or durable as gemstones such diamonds, sapphires, rubies and emeralds; however their delicacy merely adds to their desirability. The fallible properties of the natural opal add to the stones’ exclusivity and air of ephemera, and pieces featuring large natural opals are sought after.
Opal; Stones, Styles and Cuts
Opals were considered to be bad luck during the 17th and 18th century, during which time jewellers had great difficulty in setting and cutting them, due to their lack of resilience in comparison to other stones and gemstones. This rigidity is also a contributing factor in the shape of most opals we find contemporarily, as well as those we find in antique and vintage jewellery. Opals are usually cut in an ovid shape or into a cabochon, which presents the jeweller with the least possible opportunity to break the stone. This also has the benefit of being the best cut to display opals iridescence and play of colour.
Currently we have a wonderful range of vintage and antique opal jewellery at AC Silver, including an opal triplet which is a more resilient form of opal. Opal triplets are slices which are mounted on a base (onyx/quartz) and are covered by a protective layer, often made of resin, glass or transparent quartz. These give a similar appearance of a normal opal, yet have the benefit of being protected by the hardwearing surface layer.
Opal triplets are however, more affordable than true opals, as there is a larger stone content in the normal opal, and in the opal triplet there are less expensive elements contributing to the size of the stone. The visual effect of the opal triplet however, is nonetheless stunning just as with an opal, and the aesthetic properties are barely differentiated to the naked eye.
A boulder opal is an opal which has been formed around or against another non opal stone, usually an iron-stained sandstone. These slivers of opal which are visible through the host rock are so fine that it is impossible for the opal cutters to separate the opal and the rock without hugely diminishing the size of the stone.
Matrix opals are a type of boulder opal, and in the case of this spectacular opal it is certainly both a boulder opal and a matrix opal, with the thin veins of colourful opal forming in cracks and fissures in these boulders.
Due to the dark backing provided by the ironstone, boulder opals generally have a darker tone which provides a greater contrast to the vibrancy in the play of colour. The thinness of the bar of colour in boulder opals means that a high cabochoned surface is extremely rare, and boulder opals usually have a flat surface.
At AC Silver, we are able to provide our customers with an example of the very rare, high cabochoned boulder opal which has been cut into a beautiful oval shape, rather than being left as a free-from shape, like most boulder opals. This piece is an extremely rare and the setting is a very sophisticated example of the use of boulder stone.
We have truly fallen under the spell of these wonderful stones, whether in contemporary jewellery or vintage and antique pieces. Their timeless elegance coupled with their eye-catching play of colour and vibrant properties make them a magnificent choice for jewellery which brings joy to the wearer.