Since ancient times, gemstones have been treated in a variety of ways to increase their beauty. An example is the bleaching of bone or ivory to improve the color. There exist many techniques to enhance the appearance of gemstones and in fact nearly all gemstones on the market today have been treated in some way, as they have in the past. In addition, new techniques have been developed in recent years (for example, laser treatment and irradiation) and new ones are being developed all the time. This only becomes a problem if consumers are led to believe that their gemstones have not been treated, and are worth more than they really are for this reason. A partial list of the common treatments of gemstones is given below.

Agate	Dyed
Aquamarine	Heated to improve color
Black Onyx	Dyed
Carnelian Agate	Dyed
Citrine	Heated to produce color
Coral, White	Bleached white coral
Coral, "Gold"	Bleached black coral
Diamond, colorless	Laser drilled and/or filled to improve appearance
Emerald	Oiled with colorless oil to improve appearance
Ivory & Bone	Bleached to whiten
Jadeite	Impregnated with wax
Lapis Lazuli	Dyed; Impregnated with wax or oil
Pearl, natural	Bleached to improve color and appearance
Pearl, cultured	Bleached to whiten, dyed for colors
Ruby	Heated to improve color
Sapphire	Heated to optimize color
Serpentine	Dyed
Sodalite	Dyed
Tanzanite	Heated to produce color
Topaz, Blue	Irradiated or heated to produce color
Topaz (Yellow/Orange)	Irradiated to intensify color
Topaz, Pink	Heated to produce color
Tourmaline (Green/Blue)	Heated to improve color
Turquoise	Impregnated with oil or wax to enhance color
Turquoise	Stabilized with plastic to improve color & durability
Zircon (Blue, Red & Colorless)	Heated to produce color