'Indications of heating' (H) is the standard LMHC lab wording for a corundum that shows signs of heat treatment. The heating changed its color or transparency.
In more detail
Heating can leave some inclusions, such as intact rutile needles, unchanged while it alters others. If the lab sees heat-altered inclusions or spectra that show heating, it may write 'indications of (low temperature) heating'. Residues in healed fissures get their own rating.
On a grading report
Further information: indications of heating (H), with any residues in healed fissures rated.
Related terms
- No indications of heating: 'No indications of heating' (NH) is the standard lab wording for a corundum that shows no signs of heat treatment.
- Heat treatment: Heat treatment is controlled heating of a gem to change its color or clarity.
- Residues in healed fissures: Residues in healed fissures are remains of the heating process, often glassy. They stay in fissures that healed while a corundum was heated.
- Silk: Silk is a mass of fine, crossing needle inclusions, usually rutile, in ruby and sapphire.