Some Opal Facts |
Black Opal Black opal is the most coveted of all opal varities and at the high end of the market, fetching up to $500,000. The "black" in black opal means the gem has a very dark body tone. A black opal can be crystal or opaque. The rarest colour is red, next is green and orange with blue as the most common colour. Semi-black opal has an inherent darkness in it's body colour when viewed against a white background. Mid-grey stones are termed as semi-black. About 70% of the black opals come from Lightning Ridge, much less from the Mintabie opal mines. These are the two areas in Australia producing the majority of black opal. Some of the Great Colours in Black Opal! |
Crystal Opal This opal has a degree of transparency which allows the colours below the surface to be visable. Some believe the crystal varities to be the most beautiful. Crystal opals can be either light or black crystal. By definition, crystal opal is any opal, light, dark or black, clear enough to read through against a light surface but colours spring to life when viewed on any dark surface. |
Light Opal Light opal range in base colour from white to yellow. If a light opal is translucent, it is a crystal opal. The photo below is a light crystal opal carving |
Boulder Opal The term "boulder opal" describes precious opal, which occurs in deposits within weathered sedimentary rocks of the Cretaceous age in that area. It is formed as a result of silica-solution seeping into spaces in an ironrich type of sandstone, called ironstone, and then solidifying. These spaces could be large and flat, which lead to flat, clean-faced opals (boulder-opal); or the spaces could be very small and scattered in an attractive pattern throughout an ironstone nodule, which was leading to typical Koroit or Yowah-nut type opals (matrix-opal). The majority of Boulder Opal in Australia comes from Queensland. So, like other precious opal, there are many varieties of boulder opals defined on body tone, colourplay, pattern and transparency. |
A world class 22ct boulder opal, value, $178,000. |
Opal Triplets are a very thin slice of precious opal glued to a black base of glass or potch and covered with a clear natural crystal cap. Three sections. Opal Doublets are a thin section of either precious or boulder opal, glued to a glass or potch backing, no crystal cover. Two sections. Neither triplets or doublets should ever be soaked in water. Potch! What is it? Potch is defined as "Common non-precious opal without diffracted colours!" Potch is normally the host rock that the opal was cut from and a small amount remains on the surface or inside the stone after cutting. See below for more information referring to potch. *Never apply oil of any kind to any opal, oil will not soak into a solid opal and does no good! Oil can have additives that can possibly pit the surface and certainly will make a highly polished stone look dull. Extreame heat and cold are opal killers. Sudden temperature changes can cause a solid opal to crack or craze. A solid opal may be kept in a small container with just a tiny bit of water, not covered, for extended storage to protect from temperature changes. The water will not effect the opal. Never soak doublets or triplets in water. Water soaking can effect the glue attaching the crystal cap or bottom section . There are a lot of synthetic and man-made opals on the market. If any opal is exceptionally bright and has an overly regular colour pattern that looks too consistant to be natural, it may be synthetic. Often, only a detailed laboratory test can identify an opal as synthetic. The Gilson Company is one of the main producers of synthetic (or created) opals. |
On the world market, some precious opals are valued more highly per caret than diamonds. This page is dedicated to Barrie O'Leary, mentor and advisor to the opal world! |
We get a lot of questions about how to value opals based on colour. A 2CT black opal with a red colour flash that is directional, not visable from all directions is worth 1/2 of the value of a 2CT black opal with multi-blue and green colours visable from every direction it is viewed from. The colour presented alone does not set the value. The WAY the colours are presented is the most important! See below! |
Assessment of the observable play-of-colour Play-of-colour of the opal and is the most difficult factor to judge for any opal: Its brightness! * How bright is the overall play-of-colour? Its spectral range! * What range of colours is visible in the play-of-colour ? Its saturation! *How pure and vivid are the colours forming the play-of-colour Its patternI * What is the size, shape, regularity and rarity of the play-of-colour? Its consistency! * Is the play-of-colour, pattern, brightness consistent or variable over the whole face of the opal? Its directionality! * Is the play-of colour visible from all directions as the opal is rotated? Assessment of clarity! *All opals must be visually assessed for face-up clarity. Any eye visible inclusion, such as patches or lines of potch, 'webbing', the presence of 'sand spots' and/or crystals of gypsum near the surface or the opal, or the presence of ironstone (in the face of boulder opal), will effect the value of an opal. Importantly, the presence of crazing (surface-reaching cracks and fractures) in precious opal renders it commercially valueless. |
"Tear of Happiness" Magnificent Black Opal, 5.5ct, value $44,000 |
World Class Black Opal, "The Red Bouquet" , 6.1ct valued at $61,000 |
Opal may be dull and valueless, in which case it is called common opal. Common opal occurs in abundance throughout the world. One form of common opal found in association with opal of value, is "potch". In colour, potch may be white, gray, black, amber; it may be honey-coloured, watery clear, or a mixture of these colours About 95 percent of opal from the opal fields is potch. Only 5 percent is of any value. Of this 5 percent about 95 percent is mediocre grade, with only 5 percent of real value. It is this small percentage- 5 percent of 5 percent that constitutes the magnificent opal which we call "precious opal". (No wonder precious opal commands such a high dollar price). |
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With regards to photos used on our pages, in explaining the principles, please keep in mind that making photos of Opals is very difficult, much more so than of any other gem. Often the camera picks up colours we do not see, but also seems to leave out what we DO see. It should also be mentioned that Opals should always be viewed under close single incandescent light ( 12 to 15 inches away from the stone) or with the sun from over your shoulders, moving the stone in different directions for best colour flashes. |
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Note: The opals on this page are for education only, NOT for sale! |
AGIA 1-9 Body Tone Scale |
*In Black Opal the colours are often hidden at first glance, only the most expensive black opal will show all colours immediately as often can be seen in triplets. These stones start at $ 5,000 to $ 20,000 per carat and are rarely seen. |
A superb world class Semi-Black Opal with a brilliant Harequin color pattern, 37.98ct, value, $109,000 |
Len Cram. |
Andrew Cody |
Andrew Cody Photography, Rudy Weber |
Len Cram |
Len Cram |
Click here to see our best deals. |
"The Bouquet". A 49.6 ct black opal with a grand Harlequin pattern. Valued at $158,000 |
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Opals with a body tone of N-1 to N-4 are black opals. Body tone of N-5 to N-6 are semi-black and N-7 to N-9 are light opal. |
