The Laboratory Manual Harmonisation Committee (LMHC), an organisation comprising renowned gemmological laboratories, aims to standardise the wording used by gem laboratories on their reports to facilitate the understanding and comparison of reports from different laboratories.
The committee currently consists of the following laboratories:
The LMHC has released the following Information Sheets since its
establishment in 2000:
Corundum with residue from the heating process present in healed fissures and/or cavities
Members of the LMHC have standardized the nomenclature that they use to describe heat treatment in corundum and the degree to which fissure “healing has occurred, and thereside that remains within the healed fissures and cavities, following the heating of corundum.
Corundum with colour induced by lattice diffusion
Members of the LMHC have standardised the nomenclature that they use to describe the lattice diffusion of elements into corundum.
See attached PDF
Corundum with glass filled fractures and/or cavities enhancing the clarity
Members of the LMHC have standardised the nomenclature that they use to describe filled fractures in corundum. This nomenclature is used for all situations that involve the filling of fractures or cavities with glass where there are indications that the clarity of the gemstone has been altered by this process. Excluded from this nomenclature are treatments that involve the flux-assisted healing of fractures (for which see Information Sheet #1).
See attached PDF
Padparadscha sapphire
Members of the LMHC have standardised the nomenclature that they use to describe a ‘padparadscha sapphire’.
See attached PDF
Emerald - fissure filling / clarity enhancement
Members of the LMHC have standardised the nomenclature that they use to describe an emerald.
See attached PDF
Paraiba tourmaline
Members of the LMHC have standardised the nomenclature that they use to describe a Paraiba tourmaline.
See attached PDF
Corundum - No indications of heating and indications of heating
Members of the LMHC have standardised the nomenclature that they use to describe any corundum that shows no indications of heating or any corundum that shows indications of heating. See also Information Sheets 1 to 4.
See attached PDF
