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Article Index- Gemstone Enhancement and its Detection in the 2000s: Impregnation and Luster Enhancement
Gemstone Enhancement and its Detection in the 2000s:
Impregnation and Luster Enhancement
by Shane F. McClure, Robert E. Kane, and Nicholas Sturman
from GEMS & GEMOLOGY, Vol. 46, No. 3, pp. 218–240.
© 2010 Gemological Institute of America, Fall
2010
Published on JTV.com: February 2012
This is Part IV of a four part series on gemstone enhancement. See Part I, Part II and Part III.
See the end of this downloadable PDF for About the Authors, Acknowledgments, and a complete list of References.
Advances in technology and increased demand for lower-priced gemstone materials contributed to the proliferation of new treatments throughout the first decade of the 2000s. The developments that made the most difference were the diffusion treatment of corundum with beryllium, diffusion of copper into feldspar, clarity enhancement of ruby and diamond, and heat treatment of diamond, ruby, and sapphire. Gemological laboratories and researchers have done their best to keep up with these treatments, and the jewelry trade has struggled with how to disclose them. This article summarizes these developments and the methods used to identify the various enhancements.
IMPREGNATION
Impregnation of aggregate stones and other porous materials was seen more often in the first decade of the 2000s. This is largely due to increased demand for inexpensive stones, a phenomenon primarily driven by television shopping networks. The practice now extends to some unusual materials as well. A number of the gems were only usable in jewelry when they were treated by impregnation (often referred to as “stabilization”).
Jadeite.
The polymer impregnation of jadeite following the bleaching process described above was common during the last decade and will likely remain so in the future. At least one new analytical method was reported to detect this treatment (Liu et al., 2009), but its identification is still usually done with IR spectroscopy.
Nephrite.
Nephrite was reported to have been polymer impregnated after bleaching with the intent of imitating “Hetian white” nephrite (Jianjun, 2005). It, too, can be positively identified by IR spectroscopy.
Turquoise.
The greater demand for turquoise (a favorite of TV shopping networks) led to the use of more lower-quality impregnated material. Sometimes the treatment is so extensive that the material is actually a composite (figure 25), and gemological properties such as SG and RI no longer match turquoise (Choudhary, 2010; McClure and Owens, 2010). Materials used for impregnating turquoise include wax and hardened polymers. A UV-hardened polymer was identified as a filler for the first time using Raman spectroscopy (Moe et al., 2007).
Identification of this treatment is still mostly accomplished via IR spectroscopy (Henn and Milisenda, 2005; Chen et al., 2006), although many examples show veins and cavities filled with polymers that are visible with magnification.
Late in the decade, a product marketed as “Eljen” turquoise was claimed to be treated by a new proprietary process that improved the hardness and polish of soft porous turquoise. Testing showed it to be impregnated with a polymer, but it did seem harder than most impregnated turquoise, which would account for the improved polish (Owens and Magaña, 2009).
Opal.
Natural opal—a hydrous, porous material— has a tendency to dry out and crack spontaneously. This tendency is so strong in opal from some deposits that most of the material is not usable in jewelry (e.g., Virgin Valley, Nevada). To address this problem, two new treatments were reported in the 2000s: (1) oil or wax impregnation of Mexican fire opal (Gambhir, 2001); and (2) a drying-out process followed by impregnation with a silica compound, used on Ethiopian opals (Filin and Puzynin, 2009).
Other Materials.
As mentioned at the beginning of this section, impregnation was used on a number of more unusual materials during the decade. These include quartzite (Kitawaki, 2002; Juchem et al., 2006), seraphinite (Henn, 2008), and sillimanite (Singbamroong, 2005). It even extended to some manufactured materials, most notably a much-debated material from Mexico called “Rainbow Calsilica” (Kiefert et al., 2002). This material required impregnation with polymers to be useful in jewelry, as it was very porous and would not take a polish in its original state (Kiefert et al., 2002; Frazier and Frazier, 2004).
LUSTER ENHANCEMENT
This term is sometimes used to describe a treatment common to jade and some other gem materials in which a substance such as wax is rubbed on the surface of the stone to improve its appearance. The wax is only present on the surface and in depressions such as grooves in carvings, so it is not considered an impregnation. Although such substances are sometimes applied to pearls (Petersen, 2000), luster enhancement of pearls typically has a somewhat different meaning.
In the cultured pearl industry, the name Maeshori is associated with this kind of treatment (Akamatsu, 2007; Shor, 2007). Developed in the 2000s to improve the prepolishing process, it involves the use of solvents to “clean” nacreous pearls and hence produce a more lustrous surface. Various other forms of this treatment also exist (Lingyun et al., 2007). Polishing continues to be used on all types of nacreous and non-nacreous pearls to improve their salability. It takes place at all steps of the supply chain (Pousse, 2001), starting with the farmers, who often tumble their cultured pearls with walnut chips (N. Paspaley, pers. comm., 2008) and/or other materials and then polish them.
CONCLUSIONS
The first decade of the 2000s brought many new, unanticipated enhancements. Some of these—such as HPHT treatment and beryllium diffusion of corundum—usually cannot be identified by gemologists with standard equipment. In most cases, stones that might be treated by these methods must be sent to a well-equipped gemological laboratory to get a conclusive identification. Still, today’s gemologist can benefit by developing their ability to recognize when a stone shows evidence it has not been treated (particularly for rubies and sapphires) and also recognizing when they cannot tell and the stone must be sent for further testing.
It is interesting that in their retrospective of the 1990s article, McClure and Smith (2000) predicted that new filling processes would bring clarity enhancement to ruby, sapphire, and alexandrite. Three years later, at least part of this prediction came true with the development of a lead-glass filler for ruby. There is every reason to believe that this treatment, or a similar one, will soon extend to other relatively high RI materials.
Already in 2010 we have seen several new developments, including lead-glass filling of star rubies (Pardieu et al., 2010a) and a combination treatment of rubies from Mozambique that includes partial healing of fractures and partial filling with a glass that does not contain lead (Pardieu et al., 2010b).
With these developments, disclosure has become a significant topic at every trade show and gemological conference. As the trade discovered with emerald fillers (and the impact of nondisclosure on emerald sales) in the ‘90s, they neglect this subject at their peril. Consensus is critical. Discovering a treatment exists and developing identification criteria are an important start, but the trade and gemological community must work together to address the issues of what to call a treated material, how to disclose it, and how to make sure it gets disclosed. Important steps in this direction have been made, but more are needed.
McClure and Smith (2000) also predicted—correctly— that technology would advance at an even faster rate during the next decade. This will undoubtedly be the case from now on, making the unforeseen the norm in the gemological world as it is in the world at large.
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