Professional Gemologist Certification Course
Gemstone Color Change Phenomena
This oval brilliant-cut garnet displays a greenish golden brown in sunlight and a reddish, rusty brown in incandescent light. 4.13 cts, 10.7 x 8.4 mm, Tanzania. © The Gem Trader. Used with permission.
White Light and Colors
To understand how this phenomenon works, you need to learn about light and how gems get their coloration.
We know that sunlight or white light contains all colors. Pass a sunbeam through a prism and you’ll see a rainbow on a nearby wall. You can also consider light as energy. Visible light is closely associated with infrared, which heats us, and ultraviolet, which tans our skin.
Gemologists, as well as other scientists, use a spectroscope to separate light into its different components. If you were to look at the sun through a spectroscope, you’d see something like the image to the right. Each color is a slightly different wavelength of light. Thus, scientists can describe individual colors by their wavelengths or frequencies.
The Source of Gemstone Color
Most of us understand how paints work. If you want a custom color for your house, a salesperson adds the right amount of pigments to white to give you the desired shade. With very…
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.”
When you join the IGS community, you get trusted diamond & gemstone information when you need it.
Get started with the International Gem Society’s free guide to gemstone identification. Join our weekly newsletter & get a free copy of the Gem ID Checklist!