---
title: "Indications of heating: meaning in gemology"
description: "'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."
url: https://digitalgemology.com/learn/glossary/indications-of-heating
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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[Glossary](https://digitalgemology.com/learn/glossary) · Treatments and origin

# Indications of heating

Also called H

'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](https://digitalgemology.com/learn/glossary/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](https://digitalgemology.com/learn/glossary/heat-treatment): Heat treatment is controlled heating of a gem to change its color or clarity.
- [Residues in healed fissures](https://digitalgemology.com/learn/glossary/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](https://digitalgemology.com/learn/glossary/silk): Silk is a mass of fine, crossing needle inclusions, usually rutile, in ruby and sapphire.

[All 328 terms](https://digitalgemology.com/learn/glossary)