---
title: "Polariscope: meaning in gemology"
description: "A polariscope is a gem-testing instrument with a stone between two polarizing filters. With the filters crossed, it shows whether a stone is singly…"
url: https://digitalgemology.com/learn/glossary/polariscope
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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[Glossary](https://digitalgemology.com/learn/glossary) · Gem testing

# Polariscope

Also called gem polariscope

A polariscope is a gem-testing instrument with a stone between two polarizing filters. With the filters crossed, it shows whether a stone is singly refractive, doubly refractive, strained or an aggregate.

## In more detail

A singly refractive stone stays dark as it turns. A doubly refractive stone blinks: four light and four dark positions per turn. An aggregate stays light at every turn. Down its optic axis, a doubly refractive stone also stays dark, so test more than one direction.

## How we measure it

Our Polariscope computes the view by Jones calculus at 81 wavelengths, from each stone's refractive indices and measured absorption. It also has a conoscope, a red plate and an illustrative diamond strain. It is a teaching model, not a test of a real stone.

## Related terms

- [Blink (polariscope)](https://digitalgemology.com/learn/glossary/blink-polariscope): A stone blinks in a polariscope when it turns light and dark four times per turn between crossed polarizers. Blinking shows that the stone is doubly refractive.
- [Strain](https://digitalgemology.com/learn/glossary/strain): Strain is internal stress that makes a singly refractive stone weakly doubly refractive in patches. Between crossed polarizers it shows as patchy light that never goes dark all at once.
- [Conoscope](https://digitalgemology.com/learn/glossary/conoscope): A conoscope is a strain-free glass sphere set on a stone in a polariscope. It gathers light from many directions at once, so the eyepiece shows an interference figure.
- [First-order red plate](https://digitalgemology.com/learn/glossary/red-plate): A first-order red plate is a retarder in a polariscope that shows which of a stone's two rays is slower. It turns parts of the interference figure blue or yellow, and that gives the optic sign.
- [Singly refractive](https://digitalgemology.com/learn/glossary/singly-refractive): A singly refractive stone has one refractive index in every direction, so light stays one ray inside it. Diamond and cubic zirconia are singly refractive.
- [Doubly refractive](https://digitalgemology.com/learn/glossary/doubly-refractive): A doubly refractive stone splits light into two rays that vibrate at right angles and travel at different speeds. Each ray has its own refractive index.

## Learn more

- [Polariscope](https://digitalgemology.com/tools/polariscope)
- [Polariscope](https://digitalgemology.com/about/how-we-measure/polariscope)

[All 328 terms](https://digitalgemology.com/learn/glossary)