GILC 2015
Shane McClure of GIA began with an update on the activities of the Laboratory Manual Harmonization Committee (LMHC). The LMHC establishes consistent nomenclature among international lab reports but does not address standardization of criteria and testing procedures. The committee consists of seven international gemological laboratories, whose representatives meet three times per year by teleconference or in person. Information sheets that are under development include hydrophane opal, along with “pigeon’s blood” and “royal blue” designations for corundum. Topics under discussion include light sources, tanzanite/zoisite nomenclature, and the problem of stones being treated soon after a laboratory report is issued.
McClure also presented additional color designations for ruby that will be featured on GIA reports. He noted that “pigeon’s blood” would designate vivid red color on rubies with high fluorescence and low iron content, as typified by high-quality Burmese rubies. “Scarlet” and “crimson” would be used for fine-colored iron-bearing rubies with low fluorescence, in the slightly orangy to slightly purplish ranges, respectively. “Deep red” will be used for rubies of darker tone. There appeared to be different opinions among the participants about the definition of pigeon’s blood, and no clear agreement about the proposed new terms. This provoked a lively discussion as to whether “romantic” terminology belonged on lab reports, and whether the use of advantageous vocabulary was a move by some labs to gain market share.
Chris Smith of AGL spoke on the detection of low-temperature heat treatment of corundum. Smith defined “low temperature” as less than 1300°C, a treatment range where rutile (including silk) would still remain intact. The treatment has a long history and is still used to improve the color of pink, red, yellow, and orangy corundum, typically by removing purplish or bluish components. Characterization of non-rutile mineral inclusions and IR spectroscopy are keys to detecting the treatment.
Gabriel Angarita, ICA ambassador to Colombia and president of the Emerald Exporters Association, gave a presentation on residues in emeralds caused by the cutting process. He presented visual evidence that “dust” from the emeralds, laps, or abrasive powders can enter fractures during cutting and polishing, and he was concerned that they might be interpreted as clarity enhancement residues. It emerged during the discussion that although the stones might not have been intentionally clarity enhanced, the lubricating oil used in the cutting process, or the wax or nail polish used on rough to seal the fractures from dust, could be the source of the clarity enhancement being detected by gemological laboratories.
In the open session forum, participants pointed out that confidence in lab reports was waning for two reasons: (1) the inconsistency in country-of-origin and treatment determinations, and (2) the increasing prevalence of stones being altered or treated after receiving a favorable report (for instance, the re-oiling of emeralds).
The issue of hydrophane opal was revisited, with a call for nomenclature and comments, and perhaps a standardized method of assessing and communicating the degree of absorption and its impact on durability and color stability.
While trade in elephant ivory is prohibited in the U.S., the trade in extinct mammoth ivory has been severely restricted in New York and New Jersey, and on eBay. Nomenclature to distinguish the two types needs to be developed, along with awareness of treatments to disguise modern ivory as mammoth or antique to circumvent restrictions.
Another issue raised was the treatment of spinel, once considered a gemstone that was not treated. Participants confirmed the routine heating of spinel from Myanmar and Tanzania, as well as the colored (red) oiling of both spinel and corundum in Mogok. While microscopic examination does little to detect heating, photoluminescence and Raman spectroscopy are useful.
