PresidiumInstruments Gem Tester II (PGT II) with Assisted Thermal Calibration (ATC) for Identifying Diamonds/Moissanites and Common Colored Gemstones

Works as described!

Excellent Product!I love it. Worth the money.

I reached out to Presidium shortly after purchasing this because it would not *read glass...needle didn't budge one bit after calibration. I was told by other purchasers that this isn't right. I was asked to send video and more explanation (which I did)...after sending their requested information (twice), I never heard from them again. I resolved to thinking that mine just read glass as nothing as it seemed to do okay with other stones. Then, one day I went to use it and it just quit working altogether. After warming up, the needle jumped to diamond and stuck there. It wouldn't make any effort to calibrate or anything. I changed batteries to see if that was the problem. Nope...still nothing. I reached out to the company again but so far have not heard a word back. For as expensive as this machine is....IT SHOULD LAST LONGER THAN 18 MONTHS. I will update this review if I ever get a response from them but as for now, I will not recommend this product at all.

We were concerned about it's accuracy based on some of the reviews. We've had no major issues. We found it a good tool to help confirm other numbers you've gathered. It calibrated right out of the box. Read the instructions. It wants at least two calibration passes and sometimes the glass calibration test seems to drag on a bit longer than it does for the generic calibration side. It's a minute or two total, be patient. Don't test the same stone over and over. If testing loose stones buy the metal testing plate. If you are a jeweler a round bezel block works great. They work as a heat sink so your hands don't warm the stone and alter the result.Our only issue we've seen once was about two hours into the sorting marathon of larger stones with similar SG values that we believed were mostly quartz varietals. The results started being all over the board and didn't match up to common stones. Took us three stones that we moved off to the side for extra testing before we realized it had drifted. A known amethyst cabochon we had tested earlier was testing wrong. A two minute calibration and all was fixed.We tested it on a few known stones we had purchased from reputable US dealers and they all popped up as expected if they were of the testable types. This will help you narrow down your choices but for many stones by itself it is not good enough. If you have a pale blueish stone it could meter and hit the bars for tourmaline, amethyst and aquamarine on the right side of the indicators. All of these can come in very pale coloration of a similar ballpark. You would need SG and/or RI numbers to pick out which type it is.We used it to help sort out about 500ct of mixed stones. Since we knew the vague ten primary types of semiprecious stones that were in the mix sorting by color and then spot checking worked out well. Larger stones we were going to set into pendants or rings got double checked with RI and SG readings. It also helped identify a few nice odd balls that were in the lot. Gave us a class of gem to look into. For example Topaz comes in a wide range of colors. Something popping up on the Spinel and Topaz range lets us isolate what other identifiers we need to be looking at to identify it. In that case the RI should isolate which stone it actually is. If it came up Spinel I could further verify by checking the color against an expected SG for that specific color.For identifying the common sold gems often used in rings and necklaces I think it does a good job without any extra tools needed. If you were going to use it a lot I would consider buying a small cabochon or two from a US supplier. A quartz one like Citrine or Amethyst and a cheap clear topaz. Then you have known stones to test if you start getting weird results. If they test off, then you just recalibrate. If it doesn't move it's usually acrylic or a plastic. If you intend to sort gem lots and such you will need some extra testing tools to go along with this.

I purchased this device to be able to determine if gemstones I have are glass (or genuine or lab created). Once calibrated which is easy to do based on the instructions the device works well. Now...it cannot determine if a gemstone is lab created or genuine......but I'm OK with this. Lab created gemstones vs real/genuine ones will have the same chemical composition......especially if the lab created stones are high quality. They will both test the same. What was important for me was to determine if stones that I have now....or purchase.......are glass. The device does this easily. I'm very happy with it!

We are not new to gemstones. 25+ years experience. We usually test with refractometer, polariscope, spectroscope, etc. but this is portable and customer displayable.It came today and I tested 100 cut stones with 100% accuracy once I calibrated it and got a feel for pressure and 90* angle on the probe. It tested one of my prettiest cut garnets as glass! *^+}{^*! But I put that garnet under the refractometer and it is indeed glass. I hope I didn’t pay much for that rock.This machine tests thermal conductivity. Pretty reliable method to distinguish Glas from precious stone. But; a lot of specimen species have the same thermal conductivity. It’s really good for telling if that ruby ring is a ruby and not garnet or glass. It’s just a starting clue for identifying “what is this random gem?”It calibrates easily. The case isn’t protective enough, especially of the probe. Tools this low price won’t define lab vs natural - need a microscope and skills for that. Overall it’s a great buy at a reasonable price. You don’t become a Graduate Gemologist with one tool but it’s great for buyers, resellers, and collectors to confirm what you’ve got.Easy to use. Performs outstanding. A touch expensive for occasional use. Treat that probe gently, a new on will cost you. Read a book or two if you don’t know that amethyst and citrine are the same mineral species or that sapphire comes in colors.It doesn’t do opal or organics.