28 Mar 2023
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LMHC makes progress on laboratory report harmonisation
Discusses current challenges in detection of corundum treatments
By: Diamond World News Service
Mar 16 2023 7:26PM
Reference: 26795  


Holding its 30th meeting in Basel, Switzerland, the Laboratory Manual Harmonisation Committee (LMHC) has reported notable progress in the harmonisation of language used in laboratory reports. The participants in the meeting also discussed and shared new research findings on the treatments of gemstones, and in particular corundum.
The LMHC meeting, which took place on December 5 and 6, 2022, was hosted by the Swiss Gemmological Institute SSEF.
The LMHC is currently comprised of representatives from the Central Gem Laboratory (CGL), CISGEM Laboratory, DSEF German Gem Lab, Gübelin Gem Lab, GIA Gem Laboratory, The Gem and Jewelry Institute of Thailand (GIT) and the Swiss Gemmological Institute SSEF. The organisation is not formally connected to any trade association.

The main focus of the LMHC meeting was issues raised by treatments of corundum, including rubies and pink sapphires. These include the low-temperature heating and irradiation.

In recent years, an increasing number of rubies and pink sapphires have come onto the market, after having previously undergone so-called “low-temperature heating” (below 1000 °C), meant to slightly shift their colour to a better hue. Furthermore, as was reported in 2022, certain rubies and pink sapphires, some with a slightly purplish tint, have been treated by a limited number of individuals using radiotherapy equipment designed for cancer patients. This treatment can also induce a shift of the colour centre to a more attractive hue.
At the meeting in Basel, the LMHC labs decided to carry further research on these corundum treatments, in order to develop harmonised criteria for detecting their use.
 “We are very pleased to see that all laboratories represented at LMHC are constructively working together for a harmonisation on issues that are important towards ensuring consistency and clarity in gemmological lab reports,” said Dr Michael S. Krzemnicki, host of LMHC, summarising the progress made during the meeting in Basel.

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