Stone Group labs
Lab Grown Diamond testers
Bear & cara


There are many confusing choices of machine, and they can be expensive.

Question: You are considering buying OTC a 3.23 ct. E- VS1 diamond. What would the cost differences be between synthetic diamond vs a natural?

Potentially, you would save yourself upwards of $20,000 by not making the mistake of buying it as a natural. A $10k price range then is not unreasonable when you put it in those terms.

The Jewelry Industry adapted when Moissanites first came around. We went from the basic thermal diamond testers and added electrical conductivity probes to tell the differences. The problem now is how do we choose between diamond screening machines? The attached PDF nicely details comparisons of various pieces of equipment. This article was written by Harold Dupuy and Jon Phillips, and published in the Journal of Gemmology, 2019. (Courtesy of Gem-A for MJA)






SGL’s take on diamond screening devices: There are complications when a machine is trying to detect if diamond is synthetic. There can be false positives and false negatives due to post growth treatments.


We have found that it is better if your machine is designed to tell you FIRST, if your stone is a natural, or you need to refer it to further testing. Therefore, we have chosen the EXA from MAGI Labs for our screening device.

See Demonstration of its use:

This machine did not make it into the article in time for evaluations, but its degree of accuracy is on par compared to the GIA ID100. Additionally, the EXA has an Advanced Mode that puts it into the Category 3 of machines. (see Fig. 5 in article) This allows it to also distinguish between synthetics and simulants.

If there is a budget limit, you might consider the Presidium screening device sold by Stuller. Cost is $600. It utilizes SW transmission and is decent enough for basic screening.

What other things can I do to screen in the meantime?
• Does the diamond show an attraction to a rare earth magnet?
• Does it fluoresce stronger in SW UV than LW UV?
• Does it Phosphoresce?
• Does it show blue/white fluorescence with LW UV?
• Do you see Tatami straining under the polariscope?


The implications and results on the above tests are strongly noted as being “indicators” only. Conditions apply.

Please feel free to contact our lab if you have questions.


-Bear Williams is Laboratory Director of Stone Group Labs, LLC,

based in Jefferson City, MO


P.O. Box 492, Boonville, MO 65233   

(660) 882-5512


President: Roz Gordon