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OPAL (TYPES OF OPAL (Boulder Opal (Thin layers of precious opal, cut to…
OPAL
TYPES OF OPAL
Black Opal
- Have dark background colors
- Command the highest prices of all opal types
- Sell by the piece rather than by the carat
- Semi-black Opal
- Gray-base Black Opal
- Black Crystal Opal
White Opal
- Translucent to opaque white background
- Make up the bulk of commercial-quality opal
Commercial : Pale, cloudy yellow & browns w/ faint play-of-color
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Crystal Opal
Transparent to semi-transparent, exceptional play-of-color. "crystal clear"
Boulder Opal
Thin layers of precious opal, cut to include matrix
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1/3 of price of black opal of similar quality, Lack of uniformity makes it unsuitable for mass production
Fire Opal
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Background color: Transparent to translucent yellow, orange, or red, color is caused by iron
Cherry opal: lack play-of-colr, often found in Mexico
Assembled Opal
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Triplet
A backing, an opal & a clear top
Water Opal
Jelly Opal
Transparent to translucent background, can be in lots of colors but the hue is light in tone.
Might or might not display play-of-color, Lower in value because play-of-color is not vivid.
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OPAL PROPERTY
- Opal is the product of seasonal rains that drenched dry ground in regions such as
Australia's semi-desert "outback".
- Contains 3% - 10% water
- made of billions of uniform, submicroscopic silica spheres, stacked in an orderly pattern.
2 Broad Classes:
- Precious Opal
- Common Opal (Potch opal)
Play-of-color is produced by the interaction of light with opal’s internal structure of stacked silica spheres
SYNTHETICS & IMMITATIONS
Synthetics
- Pierre Gilson of Switzerland produced marketable synthetic opal in the 1970s.
- Gilson sold the process to other manufacturers, making synthetic opal at more moderate prices
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Imitations
- In late 1970s, John Slocum developed Slocum Stone, an opal imitation made of glass
- Slocum stone: effective * affordable alternative to natural & synthetic opal.
- In the late 1980s, Plastic imitation opal was first marketed in Japan.
- Opalite & Opal Essence are 2 trade names for this type of imitation opal
THE OPAL MARKET
THE OPAL MARKET
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Demand
- Commercial-quality white opal (October birthstone) dominates the US market
- Boulder opal became a popular, affordable substitute for black opal
- Strong US demand for opal doublets & truplets
- black, bounlder, white opal - $300 range per carat
Treatment
Sugar Treatment
- Heated in a sugar-saturated solution, then immersed in concentrated sulphuric acid
- Result: The phenomenal colors appear brighter
Smoke Treatment
- Opals are wrapped in paper before they're heated
- Particles of soot penetrate the opals during the heating process
Impregnation
- The opal's pores are filled with melted wax, resin, polymer, or plastic