The International Colored Gemstone Association (ICA) held its annual Gemstone Industry & Laboratory Conference on February 1 during the Tucson shows. Invited participants included jewelry trade association leaders, laboratory representatives, academic institutions, and ICA members. This year, other industry members were welcomed into the afternoon open discussion session.
Lore Kiefert (Gübelin Gem Lab, Lucerne, Switzerland), presenting on behalf of her colleague Daniel Nyfeler, spoke on age determination by radiogenic isotopes. Laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) has enabled the Gübelin Lab to use radiometric dating to test inclusions at or near the surface of materials such as corundum and emerald, which do not have radioactive atoms. When traditional methods such as observation of inclusions and growth structure and trace element analysis lead to more than one possible country of origin, radiometric dating can furnish the decisive data. U/Pb decay in zircon has been well documented as a means to establish an approximate timeline for known sapphire and emerald populations. The corundum timeline established the oldest population as African, with an age of 450–650 million years (Ma), and the youngest as Colombian, at 10 Ma. Emerald formation ranged from South Africa at 2900 Ma to Colombia at 65–35 Ma. This method is limited when the gemstone presents no analyzable inclusions or has been treated.
James Shigley (GIA, Carlsbad) presented the Institute’s latest research findings. GIA’s work with color analysis has its foundation in observation and color grading of colored diamonds. Dr. Shigley noted that the visible spectrum is not the only cause of color; in fact, the face-up appearance is influenced by about 15 factors, including the emission spectrum of the light source, the absorption spectrum of the stone, and the color sensitivity of the eye. Since humans are more adept at distinguishing differences than similarities, the use of master stones and bracketing between pairs is well suited for visual grading. GIA uses instrumentation to supplement visual grading in face-down evaluation of round near-colorless D to Z diamonds; however, fancy-color diamonds are graded face up. GIA has been working on analytical tools that can “detect” color in the same way that the human eye processes it.
Bruce Bridges (Tsavorite USA, Inc.) asked whether gems can be reliably traced from the source to the consumer. Today’s consumer wants to know where products come from and how their manufacture affects both the environment and workers. Vertically integrated companies can promote traceability and control over ethical sourcing, but the business model cannot be applied to the small-scale operations that characterize most of the industry. Bridges outlined the convoluted path from small-scale or individual miner through a series of brokers to cutting and the “end user” market, where it may go through another series of dealers before reaching a consumer. Most colored stone sources are overwhelmingly alluvial or placer deposits in remote areas, making them difficult to centralize. Traceability is even challenging at the mine, where it is not uncommon for material from a different location to be sold without disclosure. Traceability from cutting centers can improve as host countries introduce limits on rough exports and begin developing cutting facilities, which has happened in parts of Africa, South America, and Asia.
The conference proceeded to an open session for invited participants to discuss topics of concern, including:
- The increasing use of color enhancement and “anti-scratch” (silicon carbide) coatings, which are virtually invisible and sometimes too thin to be detected with instruments. With advances in nanotechnology, more research is needed to develop detection strategies.
- The inconsistent use of descriptive terminology in laboratory reports, a topic carried over from the 2015 conference. The laboratories maintained that they were responding to the demands of the trade. One participant pointed out that the terms “pigeon’s blood” and “royal blue” had no meaning in Chinese culture until about ten years ago. Since then, they have become “deeply implanted,” and a seemingly irreversible demand has been created for the level of distinction that these terms confer.
- Unethical or fraudulent use of lab reports. An example cited is the treatment of a gemstone after it had received a “clean” report. Another is the manufacture of both treated and synthetic diamonds to match an existing natural diamond report. GILC participants stressed the importance of checking reports against stones through every phase of the grading process.
- The use of “undetermined” on a lab report in regard to treatment or synthetic origin. Some participants voiced concerns that such determinations are beyond the technologies of labs, or that the word “undetermined” left untreated natural diamonds vulnerable to being matched with treated or synthetic stones.
At the conclusion of the conference, it was announced that AGTA had revised its code of ethics and principles of fair business practice. ICA is proposing to adopt AGTA’s code of ethics, due diligence protocol, and source disclosure language as a basis for its own code.