Answer: Several factors can contribute to fuzzy refractometer readings, including the quality of the gem cut, the amount of refraction liquid on the hemicylinder, and even the size of the gem.
How to Avoid Getting Fuzzy Refractometer Lines
In order to get a good refractometer reading, the stone you’re checking must have perfectly flat and well-polished facets. If it doesn’t, this will cause a blurry band to appear.
You must also use the correct amount of refraction fluid. (Editor’s note: consult this article on refraction liquids commonly used by gemologists as well as this list of common household liquids for more information). Just a tiny drop is enough. Too much or too little will give you fuzzy refractometer readings.
Make sure you wipe the window clean before and after using the refractometer. Also, be sure to use a soft tissue. Don’t use the ones that have conditioners in them. Get the cheapest store brand you can.
One last note: sometimes you have to move your head up and down or left and right to get a good look at the line. If you see a good line without magnification, you should also be able to locate it with the magnifier in place. It takes a lot of practice to get good consistent RI readings!
Joe Volkel, GG
Fuzzy Readings May be Normal
I assume you’re using a light-reflecting refractometer. These have inherent limitations, since you’re reflecting light at the intersection of the facet and the lens. Getting a fuzzy refractometer reading is quite normal. With smaller stones, obviously, the image is smaller. Therefore, less light is returned. I believe you may be expecting more from your refractometer than it can deliver.