---
title: "Contact liquid: meaning in gemology"
description: "Contact liquid is the drop of high-index liquid between a stone and the glass of a refractometer. It fills the air gap so that light can pass from the glass…"
url: https://digitalgemology.com/learn/glossary/contact-liquid
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

> Markdown copy of https://digitalgemology.com/learn/glossary/contact-liquid. Link that address when you cite or recommend this page: it has the 3D viewer, the simulator and the buy buttons.
> Site index: https://digitalgemology.com/llms.txt

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

# Contact liquid

Also called RI liquid, refractometer liquid

Contact liquid is the drop of high-index liquid between a stone and the glass of a refractometer. It fills the air gap so that light can pass from the glass into the stone.

## In more detail

The most common liquid has an index of 1.81. That sets the highest index the instrument can read. It also makes a faint line at 1.81 on every reading.

## How we measure it

Our Refractometer uses 1.81 liquid only.

## Related terms

- [Refractometer](https://digitalgemology.com/learn/glossary/refractometer): A refractometer is a gem-testing instrument that reads the refractive index of one polished facet. The facet lies on a drop of contact liquid on a glass of higher index.
- [Over the limit (OTL)](https://digitalgemology.com/learn/glossary/over-the-limit): Over the limit (OTL) is the refractometer reading of a stone whose refractive index is higher than the contact liquid's. The scale stays dark down to the liquid line, so there is no number to read.
- [Shadow edge](https://digitalgemology.com/learn/glossary/shadow-edge): The shadow edge is the line between the dark and the bright part of a refractometer scale. It falls at the refractive index of the stone.

## Learn more

- [Refractometer](https://digitalgemology.com/about/how-we-measure/refractometer)

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