Smoke treated Wollo opal from Ethiopia

Wollo (Welo) opal from Ethiopia is a new type of opal because of its ability to absorb water, which affects its transparency and opalescence. After soaking in water, most samples of this opal become transparent and lose their color. This phenomenon is reversible. After drying, the opal completely restores its color and optical effect.

 The opal from Wollo Province in Ethiopia is light and translucent with play-of-color. Some of these opals are darkened by smoke treatment to resemble natural black opals. Black opal is the rarest and most desirable. This type of treatment is stable and resistant to cleaners and solvents.

 According to the results obtained by Stone Group Laboratories in their study, the identified features of the smoke-treated opal are:

• Carbon peaks at 1150 cm-1 in Raman readings (present in most smoke-treated opals tested and absent in all untreated opals);
• play of color, predominantly in the red and green colors;
• cracks and crazing in less than ten percent of the samples;
• smoke concentration in scratches or cracks;
• Carbon (smoke) spots inside smoke-treated opal;
• Surface pitting on the reflected surface of treated opal.

The whole article “Smoke Treatment in Wello Opal” from Bear Williams, CG and Cara Williams, FGA can read here