I am looking to purchase a refractometer. I like quality and would love a Kruss or similar but my budget is not there. I have heard that less expensive Chinese manufactured refractometers work close in accuracy to the more expensive units- but there are such mixed reviews- I’d like a recommendation of one that is known to be good.
Also, am I wrong about the quality of Chinese refractometers- have the better ones been found to be accurate? Where do I source calibrated stones to test accuracy?
Yes, it is definitely just as precise and accurate as other similar refractometers such as the GIA model Duplex II. I have not used the Kruss or Rayner Dialdex, and they may allow for a little more precision and if that is required for your use, you may find a used unit in good condition (pay particular attention to the table of the prism).
The calibration for my Fable was excellent, the model 3 advertised accuracy is less than or equal to 0.003 RI. After using it for a couple years, I would not hesitate to recommend this refractometer, perhaps even above some the more expensive units due to the CZ prism which will not scratch as easily as glass.
If you require more precision, the Fable model FGR-002 has an advertised accuracy of 0.002 RI or you could spend quite a bit more and get a Kruss.
I hope this helps, Thanks, Ray
Exactly what I needed - thanks very much Ray. I’ll check for pricing on the 003 and 002 units and see what I can find- they sound like they are good value and will do a good job.
What I usually tell people is to shop on price if economy is an issue (say on ebay), since all the similar looking refractometers likely come from the same factory anyway. You want to be sure you have a polaroid disc and a sodium filter or monochromatic light source. I like to have white light capability since it gives the possibility of examining the “rainbow” for an estimate of dispersion, but this is a small point…if you have an internal monochromatic light source, I guess you don’t have this option. You also need the magnifying lens. If the instrument does not come with a liquid that is 1.80 or 1.81, you will want to buy that and need to factor that into the price. The 1.78 liquid that comes with some of the refractometers is not ideal. The most important point is to get a return privilege, since you will check the reading against a piece of quartz, which generally has an invariant RI and exchange the instrument for another if you happen to get one that does not measure quartz accurately.
The cheap Chinese models are now going for about $60 on Amazon, maybe a couple of dollars cheaper on Ebay…I’m unable to find a price for the Fables, which look nice, but may not be what you choose if they are significantly more expensive than the cheapest Chinese models…the CZ prism is nice, but a careful worker can keep the prism unscratched and in the old days people would repolish the window with some cerium oxide on a piece of cloth if it got dull.
I’m not trying to get you to go for the cheapest model, just suggesting that if you have other instruments you need to buy, price may be an issue…if you like something that costs a bit more and can afford it, go for it. I bought my refractometer when they all cost $800 and got a deal on a used Duplex II for $400…it was stolen out of my car (in my driveway in the country, imagine!) by someone who couldn’t have known what it was and I then bought an old Rayner Dialdex for $250. Always wanted one of these and they are a bit easier to read and perhaps a little more accurate. But if I lost this one, I’d be perfectly well served with a Chinese substitute. As I’ve said before, the advent of these cheaper Chinese instruments has completely changed the landscape for gemology. You no longer need to spend $4000 to outfit your gem lab! HTH, royjohn
I get good results from all three. I prefer the GIA for spot RI, especially when you have something like magnesite, gaspeite, or other minerals that exhibit birefringence blink. I find the Kruss easiest to read for flat surface measurements. The Optics Factory produces readings that are close enough to the other two that I have no concerns about using it.
