Lesson 2: Polariscope Guide, Part 2: Testing For Optic Figure and Sign


Step 3: Practical Gemology

Lesson 13

Testing for optic figure and sign is an important technique for gemstone identification. You’ll need a polariscope and a condensing sphere. If your polariscope doesn’t have built-in magnification, you’ll also need a hand-held or head-mounted magnifier.

Finding Interference Colors

Begin by setting the polariscope filters to their darkest position. Rotate the gem between the filters and look for interference colors. These are colors that aren’t normal for the gem and will resemble dispersion or the colors of a soap bubble. If you see them, touch your condensing sphere to the area of brightest color. This will reveal the optic figure.

If you have trouble finding the interference colors, look through the longest direction of the girdle while holding your condensing sphere over the girdle. This is a very small area, so you have to move your hand slowly and …

Every Gemstone Is Unique - Here's How The Experts Evaluate Them

in this training-course, discover the tools, tests & valuation process used by expert gemologists for colored gemstones, opals & diamonds

Course: Hands-On Gemology: Gemstone Identification Grading & Testing
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Skill Level: Intermediate - Advanced
Lessons: 60
Time: 480 min