---
title: "Thermal diamond tester: meaning in gemology"
description: "A thermal diamond tester measures how fast a stone draws heat from a hot tip. Diamond conducts heat very well, so it reads “diamond”."
url: https://digitalgemology.com/learn/glossary/thermal-diamond-tester
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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[Glossary](https://digitalgemology.com/learn/glossary) · Gem testing

# Thermal diamond tester

Also called thermal tester, diamond tester, heat tester

A thermal diamond tester measures how fast a stone draws heat from a hot tip. Diamond conducts heat very well, so it reads “diamond”.

## In more detail

Moissanite conducts heat almost as well. In GIA's 1997 study, every moissanite read “diamond” on every thermal tester tried. So a thermal “diamond” reading means diamond or moissanite.

## Related terms

- [Electrical conductivity tester](https://digitalgemology.com/learn/glossary/electrical-conductivity-tester): An electrical conductivity tester checks whether a stone conducts electricity. Many moissanites conduct, and most near-colorless diamonds do not.
- [Screening device](https://digitalgemology.com/learn/glossary/screening-device): A screening device separates natural diamonds from laboratory-grown diamonds and simulants. Most answer Pass (natural) or Refer (send to a laboratory).
- [Polariscope](https://digitalgemology.com/learn/glossary/polariscope): A polariscope is a gem-testing instrument with a stone between two polarizing filters. With the filters crossed, it shows whether a stone is singly refractive, doubly refractive, strained or an aggregate.

## Learn more

- [Diamond testers and moissanite: what the instruments say](https://digitalgemology.com/learn/diamond-vs-moissanite/diamond-tester-and-moissanite)

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