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

I like the instrument but using it alone in the identification of gems would be a big mistake. All test that would be normally performed should be done. You cannot rely on one instrument. It has its drawbacks.

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.

A neat tool to have in checking for diamonds (and some other stones) but hard to read between some types of gems as the identification bands overlap. It is, however, VERY good at diamond testing and if you have some knowledge of gemology it is helpful in testing other stones as well. Very good at ID-ing glass and plastic, so it is good to have for that alone when looking at old costume stuff. Calibration is easily accomplished and it holds for several operations. Battery life is sufficient for a days worth of flea-marketing.

Preface: So if you buy this, you need to have a basic knowledge of gemstones. This is not going to be the tester that is definitive if you don’t know anything about gemstones. I am not Certified in anyway, however I have a basic knowledge and this has got me a long way and using this. There are resources that you can look up including a color chart includes to help. As far as the machine itself goes, I am on my second one. I touched my first one with a large charge of Static electricity and I guess it fried it. It was approximately three years old and worked ok- I had to take the results with a grain of salt. It wasn’t very accurate. The second one seems to work better. They have to be calibrated quite frequently so make sure you learn how to do this. The needle will point to a set of gemstones, and it isn’t always the same even with the same stone so it can be a bit finicky and inconsistent on the readings. It is a handy tool to have to determine whether something is glass or gemstone though. It absolutely will not tell you whether something is created or natural.

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.

This is the go to for lots of my peers who collect or sell ewelry and gemstones. I'm very pleased with it.

I purchased this back in December 2022. I have used it moderately-somewhat heavy. There are specific stones it will confirm and then you gotta just gauge things. I absolutely would buy this again. So far, I have not needed to replace the pen. There's a lot of negative reviews about this product so I was quite skeptical at first, but I definitely don't regret this purchase at all. I would absolutely advise getting familiar with RI & SG because one testing method only to test your gems is ill-advised, especially with a machine that is limited in what it can test and confirm. I am very happy with this product. I think big points here are to make sure you are testing a flat surface of your stone (ideally the table) and be a little gentle. Keep the rubber cover on the pen at all times when not in use. Calibrate the machine regularly. Keep it clean. Clean your gems before you touch them with the probe. Keep your machine on a stable, flat surface. In my experience (which is still novice mind you), this is a great tool for testing in conjunction with other tests. My results have by and large been consistent. When they are off, I recalibrate and everything is back to consistency. EDIT: it's now the end of 2026 and this is still going strong and I haven't had issues with accuracy even now. Definitely was worth the investment. Just be careful with the pen and it will last a long time.

Great item. Be careful with tip as delicate. I’m considering buying an additional tip just in case mine gets broken

J'ai acheté ce testeur pour ma fille qui affectionne les bijoux antiques . Elle est bien contente de l'appareil et l'a utilisé pour voir si les quelques bijoux qu'elle a apportées pour son séjour sont des pierres véritables ... ou de la vitre . À son retour chez elle, elle va ''tripper au max'' à tester sa quincaillerie bijoutière . D'après ma fille , c'est un bon achat et elle est bien contente .

The Presidium was everything that I expected. Works well and the calibration instructions were easy to follow. I have only one suggestion for improvement and that is to value add by offering a US-to-Australia power plug adaptor.

لقد تم تجربة المنتج على احجار اللماس صحيحه ١٠٠٪؜ ولم يعطي نتيجه صحيحه كل ذلك اقل بنسبة ٣٠٪؜ وهاذي نسبة تخلي الواحد يتراجع او يفرط في قطعه ١٠٠٪؜ صحيحه والشي الاخر لم تتم اعادة المبلغ الى الان مايقارب ١٤ يوما واكثر ولا زلت انتظر وكل يوم اتصل ولا احد يفيدني

الجهاز جيد ويعمل دون أي مشاكل، لم استفد منه بشكل كامل لاني استخدمته لفحص الصخور والاحجار في صورتها الاساسيه وليس المجوهرات والمشغولات كما يفترض.

Muy buen producto funciona de maravilla