Gemstone Enhancement: 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 February 2012

This is Part IV of a four part series on gemstone enhancement. See Part IPart 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 theproliferation of new treatments throughout the first decade of the 2000s. The developments thatmade the most difference were the diffusion treatment of corundum with beryllium, diffusion ofcopper 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 upwith 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 of aggregate stones and other porousmaterials was seen more often in the first decade ofthe 2000s. This is largely due to increased demandfor inexpensive stones, a phenomenon primarilydriven by television shopping networks. The practicenow extends to some unusual materials as well.A number of the gems were only usable in jewelrywhen they were treated by impregnation (oftenreferred to as “stabilization”).


The polymer impregnation of jadeite followingthe bleaching process described above was commonduring the last decade and will likely remain soin the future. At least one new analytical methodwas reported to detect this treatment (Liu et al.,2009), but its identification is still usually done withIR spectroscopy.


Nephrite was reported to have been polymerimpregnated after bleaching with the intent ofimitating “Hetian white” nephrite (Jianjun, 2005). It,too, can be positively identified by IR spectroscopy.


The greater demand for turquoise (afavorite of TV shopping networks) led to the use ofmore lower-quality impregnated material. Sometimesthe treatment is so extensive that the material is actuallya composite (figure 25), and gemological propertiessuch as SG and RI no longer match turquoise(Choudhary, 2010; McClure and Owens, 2010).Materials used for impregnating turquoise includewax and hardened polymers. A UV-hardened polymerwas identified as a filler for the first time using Ramanspectroscopy (Moe et al., 2007).

Identification of this treatment is still mostlyaccomplished via IR spectroscopy (Henn andMilisenda, 2005; Chen et al., 2006), although manyexamples show veins and cavities filled with polymersthat are visible with magnification.

Late in the decade, a product marketed as “Eljen”turquoise was claimed to be treated by a new proprietaryprocess that improved the hardness and polishof soft porous turquoise. Testing showed it to beimpregnated with a polymer, but it did seem harderthan most impregnated turquoise, which wouldaccount for the improved polish (Owens andMagaña, 2009).


Natural opal—a hydrous, porous material—has a tendency to dry out and crack spontaneously.This tendency is so strong in opal from somedeposits that most of the material is not usable injewelry (e.g., Virgin Valley, Nevada). To address thisproblem, two new treatments were reported in the2000s: (1) oil or wax impregnation of Mexican fireopal (Gambhir, 2001); and (2) a drying-out processfollowed by impregnation with a silica compound,used on Ethiopian opals (Filin and Puzynin, 2009).

Other Materials.

As mentioned at the beginning ofthis section, impregnation was used on a number ofmore unusual materials during the decade. Theseinclude quartzite (Kitawaki, 2002; Juchem et al.,2006), seraphinite (Henn, 2008), and sillimanite(Singbamroong, 2005). It even extended to somemanufactured materials, most notably a much-debated material from Mexico called “RainbowCalsilica” (Kiefert et al., 2002). This materialrequired impregnation with polymers to be useful injewelry, as it was very porous and would not take apolish in its original state (Kiefert et al., 2002; Frazierand Frazier, 2004).

Carvings on turquoise


This term is sometimes used to describe a treatmentcommon to jade and some other gem materials inwhich a substance such as wax is rubbed on the surfaceof the stone to improve its appearance. The waxis only present on the surface and in depressionssuch as grooves in carvings, so it is not considered animpregnation. Although such substances are sometimesapplied to pearls (Petersen, 2000), lusterenhancement of pearls typically has a somewhat differentmeaning.

In the cultured pearl industry, the name Maeshoriis associated with this kind of treatment (Akamatsu,2007; Shor, 2007). Developed in the 2000s to improvethe prepolishing process, it involves the use of solventsto “clean” nacreous pearls and hence produce a morelustrous surface. Various other forms of this treatmentalso exist (Lingyun et al., 2007). Polishing continues tobe used on all types of nacreous and non-nacreouspearls to improve their salability. It takes place at allsteps of the supply chain (Pousse, 2001), starting withthe farmers, who often tumble their cultured pearlswith walnut chips (N. Paspaley, pers. comm., 2008)and/or other materials and then polish them.


The first decade of the 2000s brought many new,unanticipated enhancements. Some of these—suchas HPHT treatment and beryllium diffusion ofcorundum—usually cannot be identified by gemologistswith standard equipment. In most cases, stonesthat might be treated by these methods must be sentto a well-equipped gemological laboratory to get aconclusive identification. Still, today’s gemologistcan benefit by developing their ability to recognizewhen a stone shows evidence it has not been treated(particularly for rubies and sapphires) and also recognizingwhen they cannot tell and the stone must besent for further testing.

It is interesting that in their retrospective of the1990s article, McClure and Smith (2000) predictedthat new filling processes would bring clarityenhancement to ruby, sapphire, and alexandrite.Three years later, at least part of this predictioncame true with the development of a lead-glass fillerfor ruby. There is every reason to believe that thistreatment, or a similar one, will soon extend to otherrelatively 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 treatmentof rubies from Mozambique that includes partialhealing of fractures and partial filling with a glassthat does not contain lead (Pardieu et al., 2010b).

With these developments, disclosure has becomea significant topic at every trade show and gemologicalconference. As the trade discovered with emeraldfillers (and the impact of nondisclosure on emeraldsales) in the ‘90s, they neglect this subject at theirperil. Consensus is critical. Discovering a treatmentexists and developing identification criteria are animportant start, but the trade and gemological communitymust work together to address the issues ofwhat to call a treated material, how to disclose it,and how to make sure it gets disclosed. Importantsteps in this direction have been made, but more areneeded.

McClure and Smith (2000) also predicted—correctly—that technology would advance at an evenfaster rate during the next decade. This willundoubtedly be the case from now on, making theunforeseen the norm in the gemological world as itis in the world at large.