Question: I happened upon some opal in the raw when I was traveling in Honduras. There were ten pieces in a bottle filled with water. The man who sold them to me said I needed to keep them underwater. I’d like to have the opals shaped and polished for my wife as a present, but I’ve heard that they can crack if they dry out.  I’ve also heard that silicone can be injected into opals for stability. Will that help?
By International Gem Society 2 minute read
rough opals

Rough opal pieces. Photo by Deidre Wollard. Licensed under CC By 2.0.

Answer: Opals are very sensitive to sudden changes in temperature. If you purchase opals that have been stored in water, you’ll need to dry them slowly.

Opals Have a High Water Content

Before you take your opals to a gem cutter or jewelry maker, you’ll have to dry them carefully and slowly. Opals do have significant water content (sometimes as high as 21%). If they dry too quickly they may indeed crack. This is also known as “crazing.” That’s why they’re sometimes kept in water until they can be sold. It relieves the merchant of the responsibility. This is also a way to hide flaws.

Buying opals kept in water is not recommended.

Take the opals out of the bottle but don’t dry them. Put them in a zip lock bag and then put that somewhere that isn’t too hot. Leave them there for six months to a year before taking them to a lapidary or jeweler.

When you store your finished stones, keep them away from sources of heat or cold and store them in soft, moist cotton. It’s not necessary to store them in water, oil, or glycerin. Your opals will be fine as long as you don’t subject them to sudden changes in temperature or rough handling. You can consult our opal care guide for more information.

Donald Clark, CSM IMG

Silicone Treatments

Silicone isn’t normally injected into stones. However, people can smear it onto stones and then place them in a vacuum bowl. The vacuum will suck the silicone into the cracks. Although this is a simple enhancement, it’s best conducted by a professional on stones that have already been cut and polished.

Gerald Wykoff, CSM GG