Treatments, imitations and assembled stones

Treatments: As technology improves, just about every gemstone available today can be treated for color enhancement and composition durability. Opals are no exception. Treatments are typically considered to be acceptable in the trade as long as the enhancement is permanent and fully disclosed at time of purchase. Always ask if and how a stone has been treated and get all treatments clearly described on your bill of sale. The most common opal treatments are:

1. Immersion of white or gray opals in a sugar solution followed by sulphuric acid dipping. This treatment blackens the stone and is fairly accepted in the trade for bringing affordable dark stones to market. Other darkening treatments include smoke impregnation and black backing on gray stones. If an opal has been treated with these methods, avoid solvent cleaning and re-polishing.
2. Impregnation with oil, wax or plastic hides crazing, improves durability and brings out play-of-color. Of these substances, only plastic offers permanent enhancement. With these treatments, you should keep your opal away from heat, solvents and ultrasonic cleaning.

Assembled stones:
Top quality black opal can be extremely expensive. Assembled stones create a very affordable alternative to black opal and are completely acceptable in the trade. These nifty composites are called opal doublets and opal triplets.

Doublets are composed of a thin layer of top quality black opal cemented on top of a cheaper opal or glass backing. A triplet is the same process with a quartz or glass coating over the top. These stones can be identified by side-view observation. They will display a straight separation where the pieces have been cemented together. Since these stones are not all black opal, they are not sold by the carat, but rather by the piece. A beautiful, small, assembled black opal can sell for under $100.

Synthetics and imitations:
Synthetic opals are lab grown stones that can take over a year to grow and have been available on the market since the mid-seventies. They are considered "real" because they contain the same chemical makeup as natural opals. Their quality is typically very high and they make an inexpensive alternative to expensive black opal. Since a qualified gemologist is required to tell the difference between natural and synthetic stones, it is always a good idea to do business with reputable dealers in order to avoid deceptive sales practices.

If silica spheres are not used in the manufacturing of opals, the substitutes are called simulants or imitations. These replacement stones are usually made of glass or plastic and they are often called "opalite," or "slocum stone." Mostly made in Hong Kong, these fakes are fun for costume jewelry but most jewelers will fairly easily be able to spot them in a crowd.