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Colour
  • Many colours are seen in opal. Body colours can vary from white to dark blue and to black, with brown, red orange in between.
  • In recent years, a turquoise blue and a pink opal variety, owing their colour to traces of copper, has been discovered in Peru
  • More recently the opal find from Welo, Nigeria show an extensive color play in "harlequin shapes"
  • Most commecial types: white, black, fire opal
Clarity
  • Translucent, semi-translucent, opaque


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TREATMENTS
CUT
  • Play-of-Color: impregnation with oils, wax or plastic
  • Color: Dyeing or smoke impregnation: this treatment causes lighter opals to look like darker, black opals, which are considered more valuable.
  • Color: Reflective foil-backing:  this treatment darkens the gem and improves play-of-colour. Not easy to detect when opal is in jewelry
  • Color: Black paint backing: see foil backing
  • Several other treatments to stabilize the gem
  • Opals are rarely faceted because the facet edges and junctions are prone to abrasion
  • Some Mexican, Peruvian and crystal opals are faceted and these tend to exhibit a sleepy, milky appearance on colourless or coloured bodycolour
  • Most are cut en cabochon, which avoids abrasion along stark edges and are an appropriate canvas upon which to best exhibit an opal's play-of-colour



Care
  • Because opals have varying degrees of water content, they are delicate - especially when subjected to heat, temperature changes, changes in air pressure (such as in an airplane)
  • Dampened soft fabrics with no abrasive or chemical additives, or a soft bristle toothbrush doused with water

Collectors prize one-piece opals (without matrix or backing) that display strong play-of-colour. Collectors look for patterns such as "harlequin," which shows a broad flash of colours when the gem or light source is moved; "pinfire," which exhibits tiny flashes of multi-colour patches. White opals can also show these characteristics. Contra-luz opals are also collected because of their relative rarity, and their dramatic reactions to light.
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