Treatments for Turquoise:
Natural turquoise is just that. There has been no treatment of any kind. Natural turquoise can be prone to crumbling during the cutting process. However, good natural turquoise will take a fine polish.
Stablized turquoise has been treated with epoxies or acrylic resins. The chemicals are infused into the turquoise by soaking the material for a long period of time, or by subjecting it to pressure. When stabilized turquoise is cut, there is often a plastic smell.
Enhanced Turquoise (Zachary Process)
Enhanced turquoise has been treated with chemicals, then heated. The heating process eliminates any residual chemicals in the turquoise. Therefore, it is difficult to tell the difference between enhanced turquoise and natural, untreated turquoise. Unlike natural turquoise, enhanced turquoise usually does not turn green over time.
Natural Processed Turquoise
The Natural Process is a new and exciting enhancement process for turquoise. Natural Processed turquoise has been treated with completely non-toxic chemicals. This process improves the polish and color of turquoise rough, without any dyes or nasty chemicals. If Natural Process turquiose is soaked in water for 24 hours, it is impossible to detect the difference between it and natural, untreated turquoise. Natural Processed turquoise is therefore the least invasive and highest grade of treatment available for turquiose. Unlike natural turquoise, Natural Processed turquoise will not turn green over time.
Reconstituted turquoise is natural, or previously stabilized material that has been pulverized into a powder, soaked in binders and then pressed back into a solid block. Reconstituted turquoise cuts easier than stabilized material, but has a lower value. Lapis, coral and other semi-precious gems can also be reconstituted.
Block turquoise is not turquoise. Instead, it is a simulant made from plastic, ceramic, or other material. Other semi-precious stones, such as malachite, lapis, charoite, etc. are simulated with block materials.
Treatments for Other Stones:
Backed gems have a backing attached to the bottom of the stone. The backing is usually made out of some form of epoxy, or plastic resin. The backing is not seen when the stone is set in jewelry, because only the bottom of the stone has the backing material. Turquoise cabochons are often backed.
Gemstones are often heated to bring out a more desireable color. This does not change the character of the stone and is usually considered an acceptable standard process in the industry.
Some gemstones are irradiated to produce a better color. All commercial blue topaz such as Sky Blue, Swiss Blue and London Blue are irradiated. Sky Blue is usually created in a linear accelerator and very rarely contains any residual radiation. Swiss Blue and London Blue are usually created in a reactor by neutron bombardment. These stones must be tested for residual radiation before they can be legally sold in most countries. The color of irradiated topaz will not fade.
Other stones such as tourmaline, heliodor and scapolite may also be irradiated. Some of these stones may fade after treatment.