– introducing colored dyes into porous or fractured gems to change their color. Such fractures are sometimes purposely induced by heating the gem so that an otherwise non-porous material can more readily accept the dye.
1. The most commonly encountered dyed gems include:
Pearls – Dye often improves the appearance of lower–quality natural and cultured pearls by enhancing their color.
Many pearls seen in the market are dyed, as the bottle of dye-soaked pearls (left) shows, and the single pearl demonstrates (right).
Other gem materials – The process has been used since ancient times for materials such as coral, turquoise, lapis lazuli, howlite, nephrite jade, chalcedony, quartz, emerald, and ruby.
Natural chalcedony (colorless sphere to left), may be dyed with a variety of colors to achieve deeply colored materials. A slice of chalcedony (right) may be dyed with a variety of different colors. This sample was sliced further in sections that were all dyed different colors.
Coral on the left was initially bleached and then dyed.
2. Durability factors – When dye is applied to porous materials, their durability may be long-lived but is ultimately dependent on the stability of the dye itself. In gems with larger fractures, the dye can sometimes leak out under a variety of conditions. Many dyes can be removed if the gem comes into contact with a solvent such as alcohol or acetone. Some dyes are unstable with exposure to the ultraviolet in sunlight and can fade over time.
3. Detectability –A qualified gemologist can detect dyed gems in most cases.
4. Encountered in the trade – Occasionally for most gems, and frequently for colored pearls.
5. Special care requirements – When it is known that gem materials have been dyed, care must be taken to not bring them in contact with chemicals such as acetone or alcohol, which could dissolve the dyes, or have them exposed to prolonged periods of sunlight (such as leaving it on a sunny window ledge) which could cause the dyed colors to fade.
Source: Robert Weldon, www.gia.edu
To learn more about gem treatments see also: