Journal

Will my opal craze? Stability in Ethiopian opal

Guide · · Maedot

Most opal from Welo, the main Ethiopian source, does not craze. In the first detailed study of Wegel Tena opal, published in 2010, about 5% of stones cracked during sawing and preforming, and of some 3,000 cabochons one of the authors had sold since 2008, three came back cracked. Crazing was confined to transparent material, mostly crystal and fire opal. JCK traced much of the doubt about Ethiopian opal to unstable Shewa opal of the mid-1990s. Letting rough dry before you judge it, and testing gently, lowers the risk further.

What crazing is

GIA describes crazing as a fine network of cracks caused by loss of moisture, brought on by heat, very dry air or strong light. Crazed opal is fragile and sells for less, so dealers screen for it. A 2023 study of 26 opals found two routes to cracking. Opal kept in water after mining began to crack with moderate heating, up to 150 °C, as it shrank while drying. Opal kept in air for more than a year needed about 300 °C, when water trapped inside boiled.

Shewa and Welo

Opal from the Menz Gishe district of Shewa was described in Gems & Gemology in 1996. Some of it crazed under light and heat in early tests, and GIA later wrote that spontaneous fracturing made it largely unusable for jewellery. The Welo deposit near Wegel Tena, found in 2008, has behaved better. Its translucent opal withstood repeated wetting and drying far better than Shewa opal from Mezezo, and about 50 fine stones cycled between water and air, for an hour and then for up to several days, showed no change. A 2017 Addis Ababa University thesis found that hydrophane opal from Wegel Tena did not crack when heated, while non-hydrophane pieces did.

Soaking and drying

Hydrophane opal turns clearer in water and returns to its dry look in one to a few hours. That change is normal for the material and is different from crazing. Pieces in the 2010 study gained up to 10.2% in weight when soaked; in a 2016 GIA test, slices cut from one piece gained 5% to 13%, because its porosity was uneven. GIA's report on its 2018 expedition notes that water uptake can also cause crazing, and that stones respond differently because their porosity differs. JCK reported in 2015 that play of colour sometimes looks whiter after drying, or does not come back.

Testing before you buy or cut

  • Ask how the rough was kept. Rough stored in water, or shown wet, has not yet been through drying, the stage the 2023 study linked to cracking. Let it dry slowly at room temperature, away from sun and heat, before you judge it.
  • Watch it over time. The 2010 authors kept samples at room temperature and humidity and checked them; a parcel set aside in 2005 was still intact five years later.
  • Test with one drop of water. GIA's 2013 method puts a single drop on the stone under a microscope to show whether it is hydrophane. Full immersion carries more risk, because inclusions can open into cracks when the stone is saturated.
  • Look hardest at transparent pieces. Crystal and fire opal crazed most in the 2010 study.
  • Keep the cutting cool. GIA warns that high heat and sudden changes of temperature can fracture opal.

Care

Clean opal with warm soapy water only. Do not soak hydrophane opal; a 2021 GIA lab note advised against immersing it. Keep oils away too: in a 2016 GIA experiment, oil forced into Ethiopian opal under vacuum made it clearer but destroyed its play of colour. Store opal apart from harder gems, which can scratch it.

Buying from us

Every photograph and video in a selection is unedited and marked dry or wet, so you can see the state a parcel was filmed in. If material was filmed wet, ask to see it dry, or ask for samples to test before you buy.

Sources

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