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Beautiful Australian Opals

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1. While each opal is unique, there are some basic characteristics which can be used to determine an opal's market value.
2. These characteristics are, more or less in order of importance, type, brightness of fire, base color, fire color, fire pattern, rarity, cut and consistency of fire.
3. There are seven main types of opal and opal substitutes; solid opal, boulder opal, matrix opal, treated (dyed) opal, assembled opal (doublets and triplets), man-made (synthetic) opal and opal stimulants.
4. Solid opals can be all precious opal or a combination of precious and common (potch) opal.
5. Assembled opals may have backs of common opal, ironstone, jade, or glass, etc.
6. Boulder opal is a natural combination of precious opal and ironstone or other parent rock. Boulder opal consists of a line of precious opal with an ironstone back, while boulder matrix is ironstone with precious opal mixed through it.
7. Treated (dyed) matrix opal has a satin finish, looks porous under a loupe, and/or has a distinctive matrix pattern with an edge.
8. Triplets can be easily identified by the clear quartz top to the stone.
9. Doublets can be identified by the straightness of the line of color and the black paint and glued at the joint visible with a loupe.
10. Type is the single most important determinant of opal value.
11. Synthetic opals have extraordinarily bight fire, and overly regular pattern with roundish globular edges, and distinctive columns of fire when viewed from the side.
12. Imitation opals are often plastic. In most cases the flashes of color do not look like natural opal.
13. Dyed matrix has typical matrix characteristics: satin finish, looks porous, and has a distinctive matrix pattern.
14. There are two characteristics which make up the term base color; color and clarity.
15. The term black opal is frequently misunderstood. It should be used only to refer to dark base color stones meeting the criteria of the Lightning Ridge Miners Association Tone Scale.
16. Base color (tone) is determined with reference to the Lightning Ridge Miners Association Tone Scale.
17. Solid opals and boulder opals are never referred to as "natural doublets."
18. The dark base colors are referred to as black, semi-black and gray. In addition the rare red, orange, yellow, blue, green, and brown base colors.
19. Clarity refers to the degree to which you can see through an opal. The range is from transparent (referred to as crystal), through translucent (referred to as semi-crystal), to opaque (with no special terminology).
20. The brightness of the fire bouncing back from an opal is a major factor of its value, the brighter the better.
21. Lighting has a major effect on the appearance of brightness.
22. Moving the opal away from the light gives you an idea of how well the brightness holds as lighting changes. A truly exceptional opal is one that is brilliant (level 5 brightness) in and out of the light.
23. To characterize the fire colors found in an opal, the most dominate color is referred to first. Other colors which contribute significantly to the look of the stone are added. Thus, an opal which shows a dominate orange and supporting red would be referred to as having orange-red fire color.
24. An opal would be considered a multicolor stone only if it has at least three strong fire colors.
25. While every opal has a unique pattern, there are seven categories of patterns that all opal fit within: Pinfire, Flashfire, Broad Flashfire, Rolling flashfire, Harlequin, Rare patterns and Picture stones.
26. Over 90% of all opals have patterns which fit into the flashfire or broad flashfire categories.
27. The term Harlequin is frequently misunderstood and misused. It refers only to regular square or angular patches of fire closely set together.
28. Cut refers to the shaping of the opal. Most opals are cut into cabochons.
29. The most popular shape of an opal cabochon is an oval. When ovals are of standard dimensions, they are referred to as calibrated opals.
30. Poorly cut shapes include excessively fat stones, lack of a shoulder for setting, thin edges, misshapen dome, excessively thin stones, and the lack of a bevel on the bottom edge of the opal.
31. Lightning Ridge stones are cut with a heavy belly to add weight to the stone. This belly has already been adjusted of the opal's price per carat.
32. Good cut also requires that the opal should be free from scratches visible to the naked eye and that it have a smooth surface.