I am fairly new at faceting and would like suggestions on which tool would be good for checking refractive index. Brand names would be helpful.
I recomend a gemstone refractometer. There is a lot’s of brands out there and also unbranded. You budget decides ofcourse the quality of the refractometer. Regardles of brand, the most important thing is that you learn how to use it.
Dont fall for the temptation and buy a digital refractometer. They are not reliable.
I’ve actually found my digital Presidium refractometer to be quite accurate but I can see how it would not be as accurate as an analog refractometer. I had a hard time reading the analog refractometer when I worked in jewelry stores years ago and I’ve only had my Presidium for a year but it has been extraordinarily useful so far. The only downside I found was that it required a 3 mm minimum polished surface. I actually found it to be a little bit less than 3 mm but the polished surface is necessary and therefore a little time consuming but not so bad as it doesn’t matter if there are scuffs and scratches. I have been cutting stones for over 25 years and faceting for 10. I am also a jeweler/metalsmith.
The one from the online store at GIA is very reliable, not digital. Make sure you have RI liquid that goes to 1.81 and both white and monochromatic light sources.
Easiest solution to your problem is an Ebay refractometer for about $70-$100. Make sure you get the 1.80 liquid with it and get the one with the built in or screw in light source and with a polarizer. If you are finicky, you can go for the 1.81 liquid, but that will be pricey and it is a little nastier than the 1.80 fluid. It’s only a few garnets which would have a 1.81 RI that you would miss with the 1.80 fluid, and there are other ways to ID those. I like my old refractometer, which uses a white light source and a sodium filter at the eyepiece, because I can get an idea of the birefringence of the gem, but there are other ways to estimate that and none of the Chinese refractometers have that feature. At least the built in light source is handy and you don’t have to fiddle with getting a light at the right height for the refractometer window.
Don’t be worried about accuracy, as most of the instruments will be fine. Just be sure that you get a return privilege and test the instrument out on quartz, which is pretty invariant in its RI. You might query the seller if he doesn’t state that the liquid is 1.80…I noticed that some replacement liquid I bought is actually about 1.77 and I didn’t catch that until the return period was long past. You could get the digital refractometer, which actually measures reflectance, but, as some have stated, sometimes they give inaccurate readings due to polish issues. With the standard refractometer you can eventually learn to measure optic character and optic sign, which is nice to know if you have difficult ID’s on weird stones. -royjohn