Crazing

Crazing
The tendency of Opals to crack when exposed to heat or drying air. Also known as Checking.

Crazing - A network of thin irregular crisscrossing lines resembling fine cracks. This may be confined to the glaze or may go beneath causing discoloration. Delft - A blended earthenware made in Delft beginning early in the 17th c.

The uses of the opal can be restricted because of crazing. Crazing is the breakdown or deterioration of opal by the development of very fine cracks all over the surface that extend until they intersect.

A gray and white stone with black crazing (known as picasso), this gemstone is very similar in appearance to zebra jasper. However, since we do not know whether it is truly a jasper mineralogically, we've kept its descriptive market name.

It is not advisable, in fact, it is likely to be harmful, to store opals in mineral oil or or glycerin and this practice will not prevent crazing. Storage in water, although safe, has no protective benefit.

Black opal, or white hydrophane opal is occasionally treated with chemicals, smoke (carbon), or dye. Opal crazing can also be stabilized using a bonding agent such as Opticon epoxy resin which has a high refractive index.

Material can be stabilized with plastics or resins to prevent crazing. Detection of these factors must be left to experts. When you are buying you opal have a detailed description written on the invoice.

Impregnated with colorless oil, wax and resins to hide crazing
Impregnated with hardened agents to improve appearance and increase durability
Impregnated with colorless plastic to improve appearance and increase durability ...

To avoid that, always store opal jewelry wrapped in protective cloth or in its own box. If you're going to store an opal for a long period of time, storing it in a ziplock baggie with a piece of damp cloth will help prevent crazing of the stone.

Is notorious for dehydrating with time, however, causing cracking, crazing and making it less marketable than comparable material from Australia.
- Also areas in Oregon (Hyalite), Honduras, Texas (near Alpine), Idaho.

Most opals are stable if they have been around a long time, but these precautions should be acknowledged. Should you contemplate an opal purchase, be sure to inquire about the existence or absence of any "crazing." ...

crazing Condition in opal that causes it to form small, internal cracks, and in some severe cases will eventually disintegrate the opal.

See also: Stone, Rough, Color, Jewel, Cut