---
title: "Windowing: meaning in gemology"
description: "A window is a face-up area through which you can see straight through a stone. It forms where pavilion facets are too shallow to reflect light, so light…"
url: https://digitalgemology.com/learn/glossary/windowing
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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[Glossary](https://digitalgemology.com/learn/glossary) · Light performance

# Windowing

Also called window, see-through area

A window is a face-up area through which you can see straight through a stone. It forms where pavilion facets are too shallow to reflect light, so light passes out of the back.

## In more detail

Windowing depends on the angle and the refractive index together. A pavilion that works in diamond can window in amethyst. Amethyst's critical angle (40.4°) is much larger than diamond's (24.4°).

## How we measure it

On cut pages, the head-on test reads “Minor windowing” when 90% to under 99% of the pavilion reflects head-on light. The light map shows windows as leakage.

## Related terms

- [Head-on light](https://digitalgemology.com/learn/glossary/head-on-light): Head-on light is light that enters a stone straight down along its axis. Our head-on test gives the share of the pavilion whose facets are steep enough to reflect that light.
- [Critical angle](https://digitalgemology.com/learn/glossary/critical-angle): The critical angle is the angle from a facet's normal beyond which light inside a stone reflects totally. It follows from the refractive index: θc = arcsin(1/n).
- [Leakage](https://digitalgemology.com/learn/glossary/leakage): Leakage is light that enters a stone and leaves where the viewer cannot see it, mostly through the pavilion. Lower leakage is better.
- [Light map](https://digitalgemology.com/learn/glossary/light-map): A light map is a face-up picture of a cut stone, colored by the direction each point's light came from. Red is direct light, green is indirect light, blue is contrast, and a dark color is leakage.
- [Guide minimum pavilion angle](https://digitalgemology.com/learn/glossary/guide-minimum-pavilion-angle): The guide minimum pavilion angle is the shallowest pavilion at which a round still returns head-on light through the table. It is the larger of the critical angle and (180° − critical angle) ÷ 4.

## Learn more

- [Gemstone constants](https://digitalgemology.com/about/how-we-measure/gemstone-constants)
- [T73 Round Brilliant Cut](https://digitalgemology.com/cuts/t73-round-brilliant)
- [Amethyst 3D models and cutting files](https://digitalgemology.com/gemstones/amethyst)

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