Summary 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! - USB power instead of batteries - 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. Guarantee: 1 year. Detail Size: approx. 5.5 X 4 X 1.5 inches. Built-in monochromatic light 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 USB (cable and mains adaptor supplied) . Bottle of contact fluid is included. Polarising filter included. 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 a sharp '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 is more accurate than the standard model, and the divisions on the scale are clearer. 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. Limitations 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 most 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. Alternative gem testers Please note, none of these testers will distinguish natural stones from synthetic stones. "Synthetic" is a scientific term meaning 'made by man in a factory/laboratory to the same formula found in nature', the two are usually indistinguishable. Model Tests mounted stones [1] Tests Diamond Tests Moissanite TestsRuby / Sapphire Other stones Handheld presidium gem tester (GEMTEST-PGI) ✔ ✔ Shows up as diamond ✔ 31 stones Standard Presidium (GEMTEST-P2) ✔ ✔ Shows up as diamond ✔ 17 stones Presidium Duo gem tester (GEMTEST-DUO-II) [2] ✔ ✔ ✔ [3] Digital refractometer by Presidium (REFRACT-DIGI-PRESID) ✘ ✔ ✔ ✔ 55 stones [1] All testers test loose stones but not all can test mounted (set in jewellery) stones. [2] The probe / analogue meter will test mounted stones, the digital meter will only test loose stones. [3] The probe / analogue meter: 17 stones; the digital meter: 40 stones. [4] Skill and practice is required to use an optical refractometer, instructions are not included, see any textbook about gemmology…or the internet.
