– a chemical used to alter / reduce a component of, or the entire color, of a porous gem. Some gemstones are bleached and then dyed, a form of “combination treatment.”
1. The most commonly encountered bleached gems include:
Jadeite jade – Jadeite is often bleached with acid to remove an unwanted brown component from the material. Bleaching in jade is typically part of a two-step process: because acid bleaching causes the material to become slightly porous or susceptible to breakage along fractures, it is then subsequently treated with polymer impregnation to fill these open spaces to produce a better overall appearance.
These sections of jadeite show the material as it looks before and after bleaching.
Pearls – All types of pearls are routinely bleached with hydrogen peroxide to lighten and improve their uniformity of color.
Cultured pearls are routinely bleached to achieve uniformity of color.
Other materials – Some coral, chalcedony and tiger’s eye quartz may be bleached to lighten their color.
2. Detectability – Bleaching as a one-step process is virtually impossible to detect in most cases. The second step, impregnation with polymer compounds, is easier to detect by a qualified gemological laboratory using magnification and more advanced analytical techniques.
3. Encountered in the trade – Frequently in pearls and jadeite.
4. Durability factors – Acid bleaching causes a breakdown in the structure of most materials, so as a stand-alone treatment, leaves materials vulnerable to breakage. Most bleaching is followed by impregnation to improve durability and strengthen perceived color
5. Special care requirements – Bleached gems tend to be more brittle, and they may be much more porous and thereby more absorbent of human oils and other liquids. It is suggested that pearls be kept in a soft, dry environment to avoid surface damage.
Source: Robert Weldon, www.gia.edu
To learn more about gem treatments see also: