Destructive Gemstone Tests: Hot Point Testing
Gemologists use the hot point test to determine if a piece is a plastic imitation or coated in wax. Learn more about this destructive test here.
1 Minute Read
Keep in mind that hot point testing is a destructive procedure. Gemologists should conduct this test on finished gems only as a last resort for identification.
What Do You Need for a Hot Point Test?
You can purchase electrically heated hot points or you can make your own. Just insert the blunt end of a needle into a cork. To use, simply heat the needle over a small flame until the tip turns a dull red.
Heavy Liquid Warning
Do not use heavy liquids on a gem before hot point testing. In fact, it’s not a good idea to use heavy liquids for specific gravity testing on any porous stone. They will sweat out with heat and are very toxic to breathe.
Hot Point Testing for Plastic
- Heat the tool until the tip glows dull red.
- Place the stone close to your face and touch the hot point to an inconspicuous spot. (On a faceted gem, a spot near the girdle will usually do).
- Hold it there for a second or less and then smell the smoke.
Amber smells resinous, like incense.
Donald Clark, CSM IMG
The late Donald Clark, CSM founded the International Gem Society in 1998. Donald started in the gem and jewelry industry in 1976. He received his formal gemology training from the Gemological Institute of America (GIA) and the American Society of Gemcutters (ASG). The letters “CSM” after his name stood for Certified Supreme Master Gemcutter, a designation of Wykoff’s ASG which has often been referred to as the doctorate of gem cutting. The American Society of Gemcutters only had 54 people reach this level. Along with dozens of articles for leading trade magazines, Donald authored the book “Modern Faceting, the Easy Way.”
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