Gemstone Enhancement and its Detection in the 2000s:

Dyeing and Bleaching

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: January 2012

This is Part III of a four part series on gemstone enhancement. See Part I and Part II.

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.

DYEING

Although it dates back to the time of Pliny (23–79AD), dyeing continues to be seen in nearly everygem material that is porous or has surface-reachingfractures. Careful microscopic examination will frequentlyreveal the presence of dye in cracks andaround grain boundaries. In a number of porousmaterials, rubbing the surface with a cotton swabsoaked in acetone or a 10% hydrochloric acid solutioncan identify the presence of dye. In others,absorption spectra can provide proof of dyeing.

Pearls.

Dye continues to be used to improve theappearance of lower-quality natural and culturedWentzell, 2005). While the majority of dyed pearlsare nacreous, dye may also be used to make nonnacreouspearl imitations more convincing, such asthose mimicking Melo pearls (Wentzell, 2006). Ofongoing concern since the late 1990s is the detectionof dyed “golden” cultured pearls (figure 23;“Concerns raised. . . ,” 2003; Liu and Liping, 2007).Some samples present identification challenges,requiring the use of chemical analysis to detect traceelements such as iodine. Other developmentsinvolve the use of additional whitening compoundsin freshwater non-beaded cultured pearls (Shouguoand Lingyun, 2001) and the use of metallic dyesinjected into pearl sacs (“Pre-harvest colour-treatedAkoya unveiled,” 2008; Coeroli, 2010). A form ofdyeing marketed as “lasering” has also been reported.This is said to produce dark “peacock” green ordark purple colors (Liping, 2002).

Other Gem Materials.

Several other dyed gem materialswere encountered during the decade. Blue andgreen diamond crystals were found to owe theircolor to dyeing (Van der Bogert, 2005). Quartzite wasdyed red to imitate ruby (Mayerson, 2003a), whereasgreen dye was found in quartzite to resemble emerald(Milisenda, 2003). Mayerson (2003b) described aneffective simulant for high-quality jadeite: a tricolored(lavender, green, and orange) dyed and polymerimpregnatedquartzite bangle bracelet. Tan et al.(2006) used light-induced autofluorescence spectroscopyto identify dyed polymer-impregnatedjadeite. Of particular interest was dyed jadeite foundto resemble nephrite jade (Mayerson, 2004).

Low-quality red and blue corundum were foundto have been dyed (Milisenda, 2004). A parcel offaceted “rubies” purchased in Afghanistan was identifiedby Milisenda (2005b) as dyed sillimanite. Dyedblue carbonate minerals, such as magnesite anddolomite, were sold as turquoise (“Some dyed minerals.. . ,” 2000). To imitate common opal from thePeruvian Andes, marble was dyed pink and fashionedinto beads (Milisenda, 2006). Raman and IRspectra identified dyed black chalcedony in anattractive pendant set with diamonds and pearls(DeGhionno and Owens, 2003). A copper-based dyewas detected with UV-Vis-NIR spectroscopy in anatural-appearing chalcedony bead (Inns, 2007a).

BLEACHING

Bleaching is a process that uses agents such as acidsor hydrogen peroxide to remove unwanted colorfrom a gem. Only a limited number of materials willrespond to such treatment.

Jadeite.

Jadeite with brown staining caused by naturaliron compounds is often bleached with acid. This treatmentstarted in the 1990s and was categorized in theimpregnation section of McClure and Smith (2000).This is because jadeite treated in this manner must beimpregnated with polymers, as the acid damages thestructure, making it very susceptible to breakage.

This treatment has become commonplace in thejadeite market. However, the bleaching itself typicallycannot be detected, only the polymers used forimpregnation (Sun, 2001; Fan et al., 2007). The treatmentis now being used on nephrite jade as well(Jianjun, 2005).

Pearls.

Bleaching is considered an “acceptable” pearltreatment due to the difficulty of proving a pearl’sexposure to chemicals such as hydrogen peroxide.All types of pearls are routinely bleached: natural,bead cultured, and non-bead cultured. Akoya culturedpearls continue to be routinely bleached and“pinked” (Roskin, 2002b). Bleaching is also knownto be a major component of the proprietary processused to produce the “chocolate” cultured pearls (figure24) that entered the market during the decade(Zachovay, 2005; Hänni, 2006b; Wang et al., 2006c;Federman, 2007c).

Other Materials.

While there are undoubtedly additional porous materials that could be bleached, theonly other one we could find reference to is coral.Black coral is bleached to “golden” coral, which iseasily identified by its distinctive structure (Weldon,2003).

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