Turquoise is treated to enhance both its colour and durability (i.e., increased hardness and decreased porosity). As is so often the case with any precious stones, full disclosure about treatment is frequently not given. It is therefore left to gemologists to detect these treatments in suspect stones using a variety of testing methods—some of which are necessarily destructive. For example, the use of a heated probe applied to an inconspicuous spot will reveal oil, wax, or plastic treatment with certainty.

Waxing and Oiling

Historically, light waxing and oiling were the first treatments used in ancient times, providing a wetting effect, thereby enhancing the colour and lustre. This treatment is more or less acceptable by tradition, especially because treated turquoise is usually of a higher grade to begin with. Oiled and waxed stones are prone to "sweating" under even gentle heat or if exposed to too much sun, and they may develop a white surface film or bloom over time. (With some skill, oil and wax treatments can be restored.)

Stabilization

Material treated with plastic or water glass is termed "bonded" or "stabilized" turquoise. This process consists of pressure impregnation of otherwise unsaleable chalky American material by epoxy and plastics (such as polystyrene) and water glass (sodium silicate) to produce a wetting effect and improve durability. Plastic and water glass treatments are far more permanent and stable than waxing and oiling, and can be applied to material too chemically or physically unstable for oil or wax to provide sufficient improvement. Conversely, stabilization and bonding are rejected by some as too radical an alteration.

The epoxy binding technique was first developed in the 1950s and has been attributed to Colbaugh Processing of Arizona, a company that still operates today. The majority of American material is now treated in this manner although it is a costly process requiring many months to complete. Without such impregnation, most American mining operations would be unprofitable.

Dyeing

The use of Prussian blue and other dyes (often in conjunction with bonding treatments) to "enhance"—that is, make uniform or completely change—colour is regarded as fraudulent by some purists, especially since some dyes may fade or rub off on the wearer. Dyes have also been used to darken the veins of turquoise.

Reconstitution

Perhaps the most radical of treatments is "reconstitution", wherein fragments of fine turquoise material, too small to be used individually, are powdered and then bonded to form a solid mass. Much, if not all, of this "reconstituted" material is likely artificial with no natural components, or may have foreign filler material added to it.

Irradiation

Not well known, but some turquoise is irradiated to become less "chalky". This treatment is rarely disclosed. Like all irradiated gemstones, it should be tested by a Nuclear Regulatory Commission licensed laboratory before being sold in the USA.

Backing

Since finer turquoise is often found as thin seams, it may be glued to a base of stronger foreign material as a means of reinforcement. These stones are termed "Backed" and it is standard practice that all thinly cut turquoise in the Southwestern United States is backed. Native indigenous peoples of this region, because of their considerable use and wearing of turquoise, found that backing increased the durability of thinly cut slabs and cabs of turquoise. They observed that if the stone was not backed it would, for the most part, end up cracking. Early backing materials were the casings of old model T batteries and progressed to old phonograph records and most recently to the use of epoxy steel resins. Backing of turquoise is not known outside of the Native American and Southwestern United States jewelry trade. The value of turquoise of the highest quality is not discounted because it is backed and indeed the process is expected for most thinly cut American commercial gemstones