Opal is a "living" stone, which means it must be protected from heat and detergents that "dry" the gem. Opals develop crazing if they are allowed to dry out. Heat treatment is catastrophic!! In addition to cracking, loss of water causes loss of iridescence. Care must be taken when polishing and setting opals. Despite their hardness, they are prone to crazing and cracking, and loss of water content causes a noticeable loss of iridescence. To prevent this, opals are normally stored in moist cotton wool or cloth until it is time to work with them. Sometimes, an opal that has lost its opalescence may be "rejuvenated" by rehydrating the stone with water or special oils, but this may only temporarily improve the stone's appearance.
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