Gem Lab Refractometer

What is the Gem Lab Refractometer?

Editor’s note: Donald Clark wrote his review of the Gem Lab refractometer in 2006. Currently, you may find the Gem Lab refractometer (GML-501) for sale at resale shops and online marketplaces like eBay.

First Impressions

Although very similar in appearance to the ones I tested previously, the Gem Lab refractometer wasn’t the same. (This model appears to have the same case). This instrument has greater magnification, a built-in monochromatic filter at the back, and weighs more. Also, it has a transparent scale, whereas the others show the shadow against an opaque scale.

The instructions have been translated from Chinese into English, with a few errors. However, if English is your first language, you’ll be able to read them well enough. If English isn’t your first language, you might have some trouble. Review our series of articles on refractometers for more information on how to operate these tools.


The refractometer comes with a tiny bottle of RI liquid, a 10 gram refill, a small flashlight that fits into the back of the instrument, and a glass “block” for calibration. All these items fit into a padded carrying case, which itself fits into a…