Opals
Paul Carruthers Manufacturing Jewellers stock a wide range of opal in both loose stones as well as opal jewellery. We have designed and manufactured many pieces of opal jewellery.
Opal is the national gemstone of Australia. More than 95 percent of the world’s precious opal is found in Australia.
Understanding Opal
Opal, from the Greek ‘Opallos’ meaning ‘to see a change (of colour),’ is a formation of non crystalline silica gel which, 15-30 million years ago, seeped into the crevices of the host stone and through the effects of heat and pressure hardened to form this brilliant gem.
The colourful display is the result of light passing through an array of tightly packed minute spheres of silica and being refracted at different angles into the colours of the spectrum.
The size of the spheres determines the colour seen; the larger being less common and reflecting the red end of the spectrum. Hence, opals displaying red in the play of colour are regarded as more valuable. Common opal is the variety that displays no play of colour and is referred to as ‘potch’.
Australia has three different types of opal:
- Light opal from South Australia
- Boulder opal from Queensland
- Black opal from Lightening Ridge, NSW
All three kinds of opal are found along the edge of what, millions of years ago, was a vast inland sea known as the Great Artesian Basin. Opal fields stretch thousands of kilometers along this geological feature.
Light Opal
Light opals are mined at Coober Pedy, Andamooka and Mintabie in South Australia. Light (or white) opals are those which elicit a play of colour through a light or milky white translucent background.
It more commonly displays more delicate and subtle hues in shades of pink, orange and green. The most precious of the light varieties is the ‘crystal’ light opal that is transparent and colourless with flashes of the spectral colours visible.
Boulder Opal
Found in deposits in central Queensland this type of opal forms in seams and crevices through the middle of ironstone boulders. As it is only a thin layer, the opal is cut away and polished with a layer of the host ironstone on the back in order to preserve the colourful precious material.
This type of opal is most commonly cut into freeform or baroque shapes and displays vibrant green-blue colours on a dark background. Boulder opal stones can be quite large in size and are particularly suited to asymmetrical pendant and earring designs.
An interesting and rare form of boulder opal is boulder matrix, where rivulets of opal run throughout the ironstone.
Black Opal
Black Opal was discovered in the hot, dry hills of Lightning Ridge in outback New South Wales at the beginning of the 20th Cenutry.
Black (or dark) opal displays a brilliantly vibrant play of colour from within a translucent to opaque dark background. Ideally the colours visible should range across the entire spectrum but are most commonly in the greens, blues and purples. Generally black (or dark) opal is regarded as the rarest and most precious variety followed by boulder and light (with the exception of the crystal variety).
Black and Light opal is most commonly polished into oval or round domed ‘cabochons’ making it suitable for all forms of jewellery.
The greater the range of spectral colours visible the more precious the opal ie: an opal displaying violet through to red is rarer than one only showing blue-green colours.
The more uniform the size and distribution of patches of colour across the stone the more valuable. There are several different patterns including the harlequin and pinfire that are the most sought after varieties.
Valuing an Opal
Colour
The beauty of an opal is in its colour. There are three important considerations: the background colour of the opal (black, boulder, white), the variety of colours visible (a stone with a full spectrum of colours is more valuable than an opal with one colour, red colours are rarer than others) and movement of colour (as the opal is rotated, colour movement is very eye-catching and valued).
Clarity
A clear face on an opal allows its rich colours to show through. An opal with inclusions or opaque patches will not be as valuable as a clear stone because these flows detract from the opal’s colour. An opal’s colour is highly valued when it is brilliant and has bold rich tones, when it has depth into the stone and when it is consistent from different angles.
Carat Weight
Top quality opals command a price per carat comparable to diamonds.
Cut
Cutting and polishing opals is an art; a good cutter can greatly increase the value of an opal. A cabochon (rounded surface) allows more surface area on an opal. Many Queensland boulder opals are cut free form.
Solids
Solids are natural stones which have only been cut and polished, many of which have natural potch or rock backs.
Doublets
A slice of thin opal is adhered to a piece of black glass (or similar substance) and the actual opal is then polished. The opal is generally thicker than a triplet, with better quality opal, hence doublets are more valuable than triplets.
Triplets
Consist of thin slices of opal which have been adhered to a background of black glass. A dome of clear quartz crystal is then glued to the upper surface. The opal slice is so thin that it becomes totally transparent, thus the black background causes the colours to darken dramatically. The crystal dome is to protect and magnify the opal.
Need to know more?
If you’d like to have a chat about Opals, and what sort of Opals could be right for you, please feel free to contact us.