How to Prevent Opals From Crazing

Crazed Ethiopian Welo Opal   Crazing is a unique form of damage that can happen to an opal under certain unfavorable conditions. It is fairly unique in gemstones, happening generally to only opals and amber. It also happens to porcelain glaze and pottery glaze. You may recognize it in pottery as a crackled finish which can make a piece look vintage or even ancient.  

What is Opal Crazing?

Opal crazing is a type of internal and external fracturing that results in the appearance of widespread fractures throughout an opal. On the surface, these fractures sometimes resemble spider webs. (source) Other times, they look like granulated sugar designs or rough breaks, as they appear in the photo above. (source) Although opals can crack and fracture in several different ways, crazing is distinctive. A mineralogist or gemologist identifies crazing by checking the refractive indices of the surrounding material. These indices are markedly different with crazing than they are with clean fractures or breaks.   An example of crazing in porcelain glaze. Photo from Wikimedia Commons.  

What Causes an Opal to Craze?

Technically speaking, opals craze because they are not 100% solid matter. Indeed, opals contain as much as 21% water. (source) Materials that have such high water content respond to environmental pressures in unique ways. Under certain circumstances, such as high temperatures or low humidity levels, the water in an opal "moves", or literally becomes fluid. In materials science, this dynamic action of the fluids within the mineral creates the potential for internal deformation. With minor fluctuations in temperature and humidity, opals may experience an elastic deformity. Elastic deformities result in temporary changes in internal shape that reverse when conditions return to optimal. (source) However, under extreme heat or cold, or ultra-low humidity, opals succumb to what materials scientists refer to as a plastic deformity. (source) Such extremes cause permanent damage, typically resulting in crazing. Sudden temperature changes, exposure to super bright light (especially sunlight), and severe dehydration can all cause opal to craze. (source, source) Crazing most frequently occurs when an opal dries too quickly after being taken from damp conditions, or when an opal is exposed to direct sunlight for too long. (source) Sometimes vibration causes crazing. This most often occurs during the cutting and polishing phases of opal working, so long before it is set in jewelry. (source) However, ultrasonic cleaners may damage opals in this way, as well.   Crazed Opal. Photo by Collectors Weekly.  

Preventing Opals From Crazing

First of all, keep your opals out of direct sunlight and protect them from extreme changes in temperature. Also, keep them away from direct flames and other heat sources. (source) If you store your opals in a safety deposit box, safe, or vault, consider placing them into a glass container or fabric pouch, along with a damp cloth. Check on your opals monthly to prevent dehydration, as well as to prevent mold growth on the cloth. (source) Furthermore, pay attention to temperature changes going from inside to outside during hot or freezing cold weather. Wearing an opal close against your skin, beneath your jacket or scarf, should be sufficient during cold weather. (source) If the weather is hot outside, consider wearing your opal jewelry around the house for a little while before stepping out, so it at least acclimates to your skin temperature. If you're going to the beach or planning to sun bathe, keep your opal jewelry at home. At the end of the day, there is no need to store your opal jewelry in water, oil, or glycerin. (source) Simply place them in a soft fabric bag or fabric-lined jewelry box. Consider storing them wrapped in a slightly damp cloth. Just be sure to change the cloth regularly to re-wet it, and also to prevent mold and mildew growth in regions with higher humidity. While crazing does happen, as long as you take a few simple precautions your opal jewelry can last many lifetimes! ~Angela Magnotti Andrews