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Presidium Duo gem tester (model PDT-S7)

Presidium Duo gem tester (model PDT-S7)

Ref: gemtest-duo

Price: 299.50 Including VAT



Gem ID Book (£25.00 instead of £29.50) - £ 25.00

Select a free gift


This is the old (pre-2020) model (only one remaining as of late January 2020), see the new model.

We are a UK company offering fast delivery and easy telephone support. Free delivery on this item if paid by bank transfer, see details.

Bench model. A dual tester with both thermal meter and reflectivity meter.

Place the probe on the stone to operate analogue meter (the thermal meter, see detail in the extra pictures).

Place the stone over the sensor (even if it's in jewellery) to operate the digital meter (the reflectivity meter).


The thermal meter works with any stone, loose or mounted in jewellery, even uncut stones. The only condition is that the stone (and tester) must be at room temperature. It is the same as the basic Presidium model (thermal meter only), see a picture of the scale showing which stones it tests.

The reflectivity meter gives the result as a number which you look up on a chart. The chart includes 76 common gemstones, and we include two versions: the first is in numerical order of reading, the second is in alphabetical order of gemstone. Works with loose stones and also stones mounted in jewellery. The only condition is that there must be a perfectly polished, perfectly flat surface that can rest over the sensor (i.e. rings and other small items are easy, very large items will not fit).



Strong nylon carrying pouch

Instruction book

PP3 Battery

Mains power adaptor

Have you seen the fascinating article about gem testers? This will answer many questions about electronic gem testers (all electronic gem testers!) - how 'reliable' are they? How 'easy to use' are they?

In summary: no gem tester will light up with a number (or name) that tells you, with 100% certainty, the name of the gemstone. This is because nature does not make gemstones to a standard formulae, there are usually a few gemstone with the same reading. All of gemmology is a detective game. Start by using an electronic gem tester to narrow the possibilities from several to two or three, then use your knowledge to find the answer.


If you are new to gemmology I recommend the book Gem Identification Made Easy. Not only is this a good guide to gemstones, it also has details of every gem tester, including hints, tips and advanced instructions. For more details of this book, click here - special discount price if you add a book when buying this item

Not as detailed, but good guide to gemstones, beautifully illustrated, is Gemstones.