For the gemmologist the refractometer is the most important gem tester after a loupe. It measures refractive index (to what extent light is bent as it passes through the gemstone).
This product is intended for gemmologists (or those about to study gemmology) - instructions are not included.
Advanced model, has the advantages (over the standard model):
- large eyepiece enables easy viewing of the measuring scale (much easier than on a standard model!
- takes standard batteries instead of button batteries, and comes with a power supply for mains use
- the divisions on the scale are the same as the standard model but the accuracy is better
- the test-plate made of Cz (very expensive), it's harder than glass (less likely to get scratched); it also gives a wider range of reading, adding to the stones it will test - Spessartite garnet and YAG, and most Sphene.
Size: approx. 5.5 X 4 X 1.5 inches.
Range: 1.35 to 1.85
Possible error in readings: +/- 0.005
Test plate made of Cz (cubic Zirconia)
Power: 2 standard AA batteries or mains power supply (included).
2ml of contact fluid is included, just to get you started, but you will eventually need to buy a full bottle (10ml).
Is it easy to use?
A refractometer measures refraction (bending) of light as it passes through the gemstone (like poking a stick into clear water).
BASIC OPERATION: Rest the flat polished surface of the stone on the test plate, and through the viewfinder you see a scale, part of which will be light and part of which will be dark. In between the light and dark is the 'shadow edge' that marks a reading on a scale. It's a little slow and fiddly but not too difficult to master. This advanced model has the advantage that the divisions on the scale are very clear.
ADVANCED OPERATION: Not only do you get a reading, but often you will see two shadow edges, indicating a doubly refractive stone (which, itself, is diagnostic), AND advanced users can glean further information by rotating the stone to see if either or both of the shadow edges move, and by taking minimum and maximum readings for each.
Although this is an 'easy' test because you end up with a number, and you look up the number on standard charts, you will soon discover that (as with all gem testers) there are many gemstones with the same (or overlapping) readings. A refractometer will help you narrow the possibilities to a handful (maybe one or two) stones, but it will not give a "guaranteed" answer.
Some stones are out of range for this machine (their refractive index is too high to be measured) including some garnets, diamonds and some diamond simulants - though this advanced model will test for sphene and most zircon (which the standard model cannot).
Some stones have readings far too high for any refractometer, including diamond, Cz (cubic zirconia), GGG and Moissanite. A refractometer cannot be used as a diamond tester.