Turquoise can be translucent or opaque with a color that usually ranges from light medium blue to greenish blue. It is often mottled and sometimes contains dark splotches or veins of black matrix running through it. In the case of spiderweb turquoise, fine seams of matrix form distinctive web like patterns. Although matrix may be desirable and attractive, the most valuable turquoise is considered to be an even medium blue, with no matrix at all. The best color is known in the trade as "robins egg" blue. The most important market for turquoise is the American Southwest where it is commonly set in silver as the focal point in many of the Native American designs.
Because turquoise is frequently too chalky or unstable and full of holes and cracks, it is often treated with dye or stabalized with plastic.
Turquoise supposedly helps one to start new projects. Turquoise has been thought to warn the wearer of danger or illness by changing color. In the 13th century, Turquoise was thought to protect the wearer from falling especially from horses. Legend has it that the Indians believed that if turquoise was affixed to a bow, the arrows shot from it would always hit their mark. It was also believed to bring happiness and good fortune to all.
The latest proprietary turquoise treatment is commonly known in the trade as "enhanced turquoise or Zachery treated". The treatment has been used to enhance millions of carats of Turquoise for the last decade. Standard gemological techniques cannot detect it. The primary treatment involves the dissolution of quartz in an ethanol mix to be impregnated into the Turquoise and mimics a naturally occurring process that results in the turquoise being silicified or silicated.
Tests show that this process effectively improves a stone's ability to take a good polish and may or may not improve a stone's color. It also decreases the material's porosity, limiting its tendency to absorb discoloring agents such as skin oils. Examination of numerous samples known to be treated by this process revealed that Zachery-treated turquoise has gemological properties similar to those of untreated natural Turquoise and that the treatment does not involve impregnation with a polymer. Most Zachery-treated Turquoise can be identified only through chemical analysis and most efficiently by EDXRF spectroscopy. It contains significantly more potassium than its untreated counterparts, which will appear in the spectra.
The key advantages of this treatment are that the treated stones take a better polish and are more resistant to "oxidation" or discoloration over time, apparently due to a significant decrease in their porosity.
When turquoise cabs intended for use in the Native American jewelry trade are cut, they are almost always sawed thinly and then backed using some type of epoxy. An epoxy backing can be applied to give a thin stone both height and strength, along with a flat bottom for convenient use in a bezel setting. Backing turquoise is generally an American concept that started in the 1950s for a number of reasons.
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