Dyed opal

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Dyed opal treatments

Many Ethiopian opals are sold in their natural state, and some are dyed opal treated. Their porosity makes them good candidates for dye, smoke, and sugar/acid treatments.

All of these treatments, when disclosed, reduce the price of the opal to much less than natural opal with the same appearance. When undisclosed they can deceive inexperienced buyers and sometimes even experienced buyers.

Hydrophane opals

Hydrophane opals, like those found in Ethiopia, are easy to dye because their porosity naturally absorbs liquids. People who know opal can identify dyed opal on-sight when an outrageous color is used.

However, the practice of slightly enhancing an opal’s body color with dye can be much less obvious. In these cases, dye treatments can often be detected with microscopic examination or by cutting into the opal to see if the color is concentrated near the surface.

Some large buyers of cut opal or finished jewelry require vendors to provide samples of the opal rough when making large purchases. The samples are used for testing and comparison to assure that the finished stones and jewelry they are purchasing have not been treated.

Dyed opal color enhancements can increase the marketability and price of the opal if not obvious or disclosed. For this reason, if a buyer wants natural-color opal, testing to confirm that the color is not caused by dye is important.

Dyed treatment is not durable

Dyed treatment is not durable, exposing the stone to the day light, the color will have almost completely disappeared after a few months.

Opal

Opal is a hydrated amorphous form of silica SiO2·nH2O, its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals.

It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt. Opal is the national gemstone of Australia.