Destructive Mineral Tests: Dye Testing

Exhaust the Alternatives Before Dye Testing

You can often distinguish dye in a mineral with a microscope. See our article on identifying inclusions found in enhanced stones for more information on this. Remember, dye testing is a destructive test, so always examine your specimen with a microscope first.

The testing procedure presented here is a last resort, in cases where the microscope exam proves inconclusive.

Frequently Dyed Minerals

Many soft, porous gems and minerals often receive dyes. Lapis lazuli is one of the most common recipients of dyes. Any dark lapis is suspect and needs testing. The same holds true for turquoise.

Dye Testing Procedures

• Choose an inconspicuous location on your specimen for your test. (If the stone is faceted, choose a point near the girdle).
• If you're testing a strand of beads, make sure you don't get any fluid on the cord. Some of the chemicals used for identification will damage cords.
• Dip a cotton swab in acetone and rub it quickly on an inconspicuous area of the gem. Clean the stone immediately with a damp cloth.
• Check the swab for dye. If there's a colored residue on the swab, you can be certain the stone is either a dyed natural gem or a non-natural imitation.
• If the swab is clean, you could still be looking at a dyed natural gem with a wax coating. Conduct a hot point test to see if the gem is waxed.

Although acetone is the most useful substance for testing, it won't pick up all dyes. If your swab comes back clean, repeat the test with denatured alcohol and again with vinegar. If the swabs are clean after these tests, you can say with assurance that the gem has natural color.

Dye Testing NOT Recommended for Black Pearls

Although you may occasionally find dye tests recommended for black pearls, choose a safer alternative. Natural black pearls fluoresce under longwave ultraviolet (UV). Dyed ones don't. Thus, UV testing is preferable, as there's no danger to the pearls.

Editor's Note: The original article has been updated and adapted for the Mineralogy Certification course.

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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