Step 3: Practical Gemology

Lesson 16

Since diffusion treated gems are so common, gemologists must learn how to identify these treatments.

Diffusion treatment usually involves applying color to a colorless cut gem by introducing chemical impurities at an atomic scale. Some sapphire gems receive this treatment to improve their color. We gemologists now face a new beryllium/lattice diffusion process that appeared on the market in 2002 involving padparadscha sapphires. However, we can detect it using established methods for identifying diffusion treated gems.

The Immersion Method for Identifying Diffusion Treated Gems

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 sapphire. Keep in mind, many immersion fluids can be harmful. Although safer alternatives may be