How to Test for Diffusion Treated Gems
How to Test for Diffusion Treated Gems

Professional Gemologist Certification Course

How to Test for Diffusion Treated Gems

The Immersion Method

Setting Up

This inspection process is simple. First, you need a substage, diffused light source. A microscope, polariscope, or even a flashlight will do. If you don't have a frosted glass plate, simply lay a tissue over the light.

Next, place a small glass beaker over the light and fill it partially with an immersion or refraction fluid. Choose a liquid with a refractive index (RI) close to that of the test stone. For example, methylene iodide has an RI of 1.74, ideal for corundum stones like ruby and sapphire.

Keep in mind that many immersion fluids can be harmful. Although safer alternatives may be available, always exercise caution.

Immersion Fluids

Use the following chart to find a good immersion liquid for your gem.

Immersion FluidsRI
Water1.33
Alcohol1.36
Corn oil1.47-1.48
Olive oil1.44-1.47
Glycerin oil (glycerol)1.47
Almond oil1.45-1.47
Clove oil1.53-1.54
Wintergreen oil1.54
Anise oil1.54-1.56
Cinnamon oil1.59-1.62

Examine Your Gem

Once you've set up your equipment, immerse the gem in the fluid and examine it.

When you put a stone in a liquid with the...


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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