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GradingDec 17, 2018
Lab Group Updates Padparadscha Requirements, Treatment Vocab
The Laboratory Manual Harmonisation Committee clarified on a disqualifying trait for padparadscha sapphires and how lab reports should address new corundum treatments.
Lucerne, Switzerland—The Laboratory Manual Harmonisation Committee has further harmonized the color description for padparadscha sapphires and vocabulary regarding new treatments on lab reports.
The LMHC recently had its 29th meeting, hosted by Gübelin Gem Lab in Lucerne, Switzerland, on Nov. 14 and 15.
The committee currently is comprised of representatives from the Central Gem Laboratory (CGL), CISGEM Laboratory, DSEF German Gem Lab, Gübelin, the Gemological Institute of America, the Gem and Jewelry Institute of Thailand (GIT) and the Swiss Gemmological Institute SSEF.
During the meeting, the first major point the labs agreed to clarify was the use of the term “padparadscha.” They deemed that the term can’t apply to a gemstone if the color is unstable and shifts to pink when exposed to a color stability test.
When asked why the LMHC wanted to clarify this point, Lore Kiefert, chief gemologist at Gübelin as well as host of the meeting and past co-chair of the LMHC, said the decision came after the SSEF discovered issues with the color stability of some padparadschas.
“If you buy a gemstone as a padparadscha and several days later it is a pink sapphire, you have probably overpaid, so we need to make a comment about the color stability,” she said.
The Laboratory Manual Harmonisation Committee said that corundum with an unstable color, as shown in this photo, is not qualified to be called “padparadscha.”
The LMHC currently defines padparadscha as a “a variety of corundum from any geographical origin whose color is a subtle mixture of pinkish orange to orangey pink with pastel tones and low to medium saturations when viewed in standard daylight.”
Kiefert said that definition won’t be narrowed any time soon, given that each market has its own perception of what comprises a padparadscha. As it is, she added, it already has taken a great amount of time to come to the current conclusion.
However they are looking into a color communication system to see if they can define the same borders for colors at all of their labs.
The LMHC also addressed issues raised by new treatments, including the low-temperature heating of corundum and a new sapphire heat treatment that has been incorrectly named High Pressure-High Temperature (HPHT) within the trade.
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In regards to the latter, the LMHC said current data available from member labs shows the treatment is essentially a form of heating and, as a result, is similar to most known heating techniques.
For this reason, it doesn’t require a specific reference on lab reports beyond the standard disclosure of heat treatments, though the committee did stress that heat treatments can create fissures or expand pre-existing fissures in a gemstone, especially when high temperatures are applied, possibly having a negative impact on the stability of the heated stone.
The LMHC said it also kicked off a project aimed at harmonizing the use of color descriptors and trade color terms at its member labs, though there is no additional information available yet regarding what that might include or what the timeline might be.
The LMHC also approved new info sheets about organic fissure-filling in gems and hydrophane opal. Kiefert said the two sheets were already in existence but were just now finalized.
The LMHC usually meets once per year and has tentatively set its next meeting for November 2019.
The ICA has scheduled its next Gemstone Industry and Laboratory Conference, addressing similar issues, for the 2019 Tucson gem shows.
The LMHC has no formal ties to any trade organization. The info sheets it creates are a result of harmonization attempts of its member labs and are also meant to help the trade understand the wording on LMHC member reports. They also are meant to serve as recommendations for other labs that may come across the same issues.
All LMHC info sheets can be accessed on its website.
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