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

Step 3: Practical Gemology

Lesson 13

optic figure and sign - interference colors
A gem positioned so its interference colors are visible.

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 …

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