Step 2: Advanced Gemology

Lesson 3

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.

sunlight viewed through a spectroscopeGemologists, as well as other scientists, use a spectroscope to separate light into it’s 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…