The American Gem Trade Association has published an excellent industry information guide for natural gemstones, color and clarity enhanced (treated) natural gemstones and man-made stones including care and handling recommendations.
This document is a 350KB PDF file readable in Adobe Acrobat
Throughout the ages, colorful rocks and gems have been appraciated for their beauty and used by mandkind for adornment. It is only natural to expect the finders and dealers of these treasures to want them to look their best, so efforts to enhance gems appearance were widely pursued. Various techniques have developed over the centuries such as heating, oiling, bleaching, irradiating and dying. Some of these techniques are centuries old and traditional, while other are quite new and very high tech.
