Most gemstone material - both cut stones and rough, is enhanced. For some gemstones, the enhancements have relatively no effect on value, are permanent, undetectable to the human eye and often difficult to see under a microscope as well.
Enhancements increase the available supply of gemstones, thereby increasing their affordability as well. Giving Mother Nature a little hand has produced some wonderful results that imitate some of the natural processes that accompany geologic formation (such as heat and irradiation) of gemstones.
What are the treatments?
Gem treatments, or enhancements, are human initiated processes that improve the appearance and durability of a gemstone. Heat treatment, using high temperature to change the appearance or color of a gem, is one of the oldest and most common enhancement processes; it has been used for thousands of years.
Temperature Treatment
Heat treatments are used to lighten, darken, deepen, or even completely change gemstone color. The temperatures and length of time vary, but temperatures range from 157-1900 degrees C.
Heat treatment works like it sounds- the stones are heated.
Irradiation Treatment
Irradiation affects only a gemstone's color. Subatomic particles, such as gamma rays, are used to bombard the electrons of the gem, causing them to be knocked loose, and captured by other atoms. The light-absorbing pattern is thereby changed and as a result, so is the color. In the case of gamma rays, no leftover radioactivity remains. Many gem laboratories regularly check irradiated gemstones to ensure that they are not radioactive.
Chemicals
This is the largest group of enhancements with the greatest number of effects on the gemstones.
1. Bleaching
2. Dyeing
3. Diffusion
4. Oiling
5. Impregnation
Bleaching and Dyeing
Just as it sound: chemicals are used to remove color; or just the reverse, dyeing adds a chemical agent to change or deepen color. Dyeing works better done with porous substances such as lapis lazuli.
Diffusion
Chemicals are used instead of heat. The chemicals penetrate a shallow layer of the surface, become part of the crystal structure, and change color superficially. Sapphires and rubies can be diffusion treated.
Oiling & Impregnation
This enhancement involves the filling of surface reaching fractures with oil or a plastic polymer substance to make them appear less noticeable. Emeralds are routinely oiled and jadeite is commonly polymer impregnated.
Last Update: 27 Nov 2008