Turquoise

:This article is about the gem. For the colour, see turquoise (color) and cyan.

Treatments

Turquoise is treated to enhance both its colour and durability (i.e., increased hardness and decreased porosity). Historically, light waxing and oiling were the first treatments to be used (since ancient times), providing a wetting effect (thereby enhancing the colour and lustre); this treatment is more or less acceptable by tradition, and because such material is usually of a higher grade to begin with. Conversely, the later development of pressure impregnation of otherwise unsaleable chalky American material by epoxy and plastics (such as polystyrene) and water glass—also producing a wetting effect in addition to improving durability—are rejected by some as too radical an alteration. Plastic and water glass are technologically superior to oil and wax in that the former treatment are far more permanent and stable, and can be applied to material too friable for oil or wax to be of sufficient help; such material is termed "bonded" or "stabilized" turquoise. The epoxy

Related Topics:
Hardness - Porosity - Epoxy - Plastic - Polystyrene - Water glass

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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 impregnation most American mining operations would be unprofitable.

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Oiled and waxed stones are also 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.) Likewise, 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 purists—especially since some dyes may fade or rub off on the wearer. Dyes have also been used to darken the veins of turquoise. Perhaps the most radical of treatments is "reconstitution", wherein supposedly fragments of fine material too small to be used singly are powdered and then bonded to form a solid mass. Much (if not all) of this "reconstituted" material is likely a complete fabrication (with no natural components), or may have foreign filler material added to it (see Imitations section). Another treatment—the details of which remain

Related Topics:
Prussian blue - Imitations

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undisclosed—is the so-called Zachery process, named after its developer, electrical engineer and turquoise trader James E. Zachery. This process claims to use only medium grade material at a minimum, leaving the turquoise harder and with a better colour and lustre.

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As the 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 are termed doublets and can be very deceptive in certain jewellery setting styles (such as closed back and bevel settings). Some turquoise is cut with the mother rock serving as a base; these are usually not considered doublets but may have an intrinsic value lower than that of "whole" stones. Doublets, like the aforementioned treatments, are legal provided they are disclosed to the customer before sale.

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As is so often with gems, full disclosure is frequently not given; it is therefore left to gemmologists 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.

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