Pinfire Opal — The Pattern Variety
Pinfire Opal — The Pattern Variety
Precious opal whose play-of-colour appears as small scattered flashes against a darker body
Pinfire opal is a trade name for precious opal whose play-of-colour is composed predominantly of small, scattered points or short flashes of spectral colour against a darker body — typically the black or dark grey of Australian Lightning Ridge material. The variety occupies the most populous segment of the precious-opal market and is the entry-level expression of the higher-priced broad-flash, rolling-flash, and harlequin patterns. The colour-patch size is small because the domains of ordered silica spheres responsible for diffraction are small and broken up across the stone; the saturation, contrast, and spectral range of the colour points determine commercial quality.
Composition and structure
All precious opal is hydrated amorphous silica, SiO2·nH2O, with water content typically 6 to 10 percent by weight, organised into a packing of submicroscopic silica spheres of uniform diameter. The diffraction of visible light by this ordered array produces play-of-colour, with sphere diameter setting the diffracted wavelength and domain size setting the colour-patch size. Pinfire opal forms where the ordered domains are small and discontinuous; broad-flash and harlequin opals form where the domains are larger and more uniform across the stone.
Pinfire body colour ranges from dense black to grey to colourless crystal, and the contrast between body and play-of-colour is one of the principal commercial variables. Black-body pinfire from Lightning Ridge is the most desirable expression; white-body pinfire from Coober Pedy is more affordable and more common.
Sources
The principal sources of pinfire opal are the New South Wales fields of Lightning Ridge for black opal pinfire, the South Australian fields of Coober Pedy and Andamooka for white and crystal pinfire, and Welo (Ethiopia) and Querétaro (Mexico) for volcanic and hydrophane pinfire material. Australian sedimentary opal is the historical reference, with Lightning Ridge production going back to the late nineteenth century. Welo pinfire material reached the market only after 2008 and remains differentiated from Australian product by its hydrophane behaviour and specific gravity.
Cutting and care
Pinfire opal is cut almost exclusively as cabochon to maximise viewing area and to display the colour points across the dome. Cutters orient the rough so that the colour-bearing layer lies parallel to the base of the cabochon and the play-of-colour is fully visible from the face-up position. Doublets and triplets — opal slices bonded to a backing of black potch or chalcedony — are common in lower-priced material and must be disclosed.
Hardness at 5.5 to 6.5 and the presence of structural water make opal vulnerable to thermal shock, dehydration, and mechanical impact. Care recommendations are conservative: avoid prolonged dry storage, avoid ultrasonic and steam cleaners, and prefer bezel or protected prong settings over exposed claw mounts in ring designs.
In the trade
Pinfire opal is the most widely traded pattern variety in commercial opal, with a global price range from a few dollars per carat for low-saturation white-body material to several thousand dollars per carat for top-quality black-body stones with a full spectrum of colour points. The pattern's commercial importance is greater than its position in the pattern hierarchy might suggest, because pinfire stones populate most jewellery price points and most retail offerings.
Buyer guidance focuses on the brightness and contrast of the colour points, the proportion of the dome covered by play-of-colour, the spectral range present, and the body colour. Pinfire stones with full red and orange points against black body are among the most desirable opals at any price.