General Information

What is it?: This handy little piece of equipment tests a gemstone's ability to slow down or bend light. The amount of slowing down it does to a beam of light is called the refractive index, which is a number assigned to a scale we will see in a minute. And while some gemologists think that a refractometer is used just for gemstone identification, truth is that long before it was used for the identification of gemstones, the refractometer was used to set prescriptions on eye-glasses, and (get ready for this) to tell when grapes are ready to be picked to make wine...based on the refractive index of the grape juice. For our purposes we will work with the idea of gemstones...although I know a lot of gemologists who work on their own to test a lot of wine. But enough of that...on to the study of the refractometer.

How does it work?: The refractometer works by the use of a glass hemicylinder inside that has a flat surface extending into the body of the refractometer as shown above. When light is introduced into the back of the unit, it travel through the glass hemicylinder and up to the gemstone, where the stone is in optical contact with the glass by use of a refractive index liquid. This liquid keeps air from between the stone and the glass hemicylinder and allows light to travel at the same speed through the glass, gets refracted by the gemstone, and then back through the glass hemicylinder to the viewing lens. The amount of slowing down or bending of the light that the gemstone does to the light beam, causes a light and dark area joined by a thin green line as shown below. This green line is the refractive index reading of the gemstone.

How do I use it to get a refractive index? You must use caution when placing a gemstone on the glass hemicylinder because the glass is very soft and will scratch easily. Once scratched it is very difficult to get it repaired. Here is the method you should use:

 N Warning!: The refractive index liquid used in a refractometer is highly toxic and should not be used in a closed room. The liquid should be washed off immediately if you get is on your skin.

Once you have the stone in place...move your light source, such as a pen the back of the refractometer and focus the beam inside the back until you can see light inside the view lens. then......

You can purchase a professional quality refractometer at a special visitor price in the YourGemologist Gemology Equipment Store by clicking on this link: YourGemologist's Refractometer

 © Copyright 2014 YourGemologist LLC All Rights Reserved. Please read the fine print below:

The information contained in this website is offered free of charge to anyone wishing to learn more about gemology. The information may be downloaded by any student, consumer, or jeweler for your own personal study and use. None of this site can be downloaded for posting on another website or server for any reason. It will be a violation of the copyright for anyone to copy, duplicate, distribute, and/or re-print this material in any format or any medium without written permission. Nor can anyone post this information on a for-profit website without written permission. That will ruin it for everyone and cause the entire site to be erased and canceled. Please honor this copyright for the good of everyone else.

Robert James FGA, GG.....YourGemologist

Return to Study of Gemology

Return to Home Page