Ethiopian Opal Treatments

Ethiopian opals, many of them are sold in their natural state. Others are treated, for example, dye, smoke and sugar/acid treatments. All of these treatments make the opal less expensive, and when the opal is natural it is far more expensive than the treated ones. The treated opals can cost less or more than the natural opals this depends on the cost on the process this opal went through. The first treatment I will talk about is the dye treatment, then the smoke treatment, and finally the sugar/acid treatment.

Dye Treatment

Hydrophane opals, like those found in Ethiopia, are easy to dye because their millions of tiny holes it, naturally absorbs liquids. When dying the opal is like it is sucking all the color up, because of the pores inside of it. People, who know opals, can identify dyed opal on-sight when an abnormal color is used. For example, a neon blue color is easy to tell that the color is a fake but other people feel like it is natural. However, the practice of slightly improving an opal’s natural 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 the seller’s to provide samples of the opal rough when making large purchases. The samples are used for testing and comparison to make sure that the finished stones and jewelry, they are purchasing have not been treated. Color enhancements can increase the marketability and price of the opal if it is not obvious. For this reason, if a buyer wants natural-color opal, testing to confirm that the color is not caused by dye is important.

Smoke Treatment

Smoke is a suspension of very fine particles in air or gas. Fine smoke particles can enter the pore spaces of an opal and change its natural color. The smoke treatment can be done by wrapping the opal in paper and heating the paper to a temperature that produces burning. The burning paper releases fine particles of black soot; a black substance, that enters the pores of the opal and darken its color. The darker color contrasts with the opal’s play-of-color, making it appear stronger and more obvious.

Smoke treatment can sometimes be detected by looking for black soot particles during microscopic examination. These can often be seen individually, or in concentrations along cracks within the opal. Laboratory tests, such as Raman microscopy, have the ability to detect smoke treatment because they can detect carbon, which is normally absent in opals of volcanic origin.

Sugar/Acid Treatment

The sugar/acid treatment is done by soaking opal for a few days in a warm solution of sugar water, then submerging the opal in concentrated sulfuric acid. The acid melts the sugar in the pore spaces of the opal, producing dark-colored carbon particles and stains. This imparts or darkens a gray, black, or brown color in the opal. Like smoke treatment, these can be detected by microscopic examination or by laboratory tests for carbon.