---
title: "No indications of heating: meaning in gemology"
description: "'No indications of heating' (NH) is the standard lab wording for a corundum that shows no signs of heat treatment."
url: https://digitalgemology.com/learn/glossary/no-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

# No indications of heating

Also called NH, unheated, no heat

'No indications of heating' (NH) is the standard lab wording for a corundum that shows no signs of heat treatment.

## In more detail

It is the lab's finding from the stone's inclusions and spectra, not a guarantee. Some heating conditions leave certain inclusions unchanged. 'Unheated' is the trade word for the same claim.

## On a grading report

Further information: no indications of heating (NH).

## Related terms

- [Indications of heating](https://digitalgemology.com/learn/glossary/indications-of-heating): '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.
- [Heat treatment](https://digitalgemology.com/learn/glossary/heat-treatment): Heat treatment is controlled heating of a gem to change its color or clarity.
- [Silk](https://digitalgemology.com/learn/glossary/silk): Silk is a mass of fine, crossing needle inclusions, usually rutile, in ruby and sapphire.
- [Origin report](https://digitalgemology.com/learn/glossary/origin-report): An origin report gives a lab's opinion on the country or region where a gem was mined.

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