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Presidium Duo II gem tester (model PDT-II)

Presidium Duo II gem tester (model PDT-II)

Ref: gemtest-duo-II

Price: 359.00 Including VAT



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

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New model for 2020.

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


POWER: five AA batteries (or optional mains adaptor)
SIZE: height 85mm, width: 77mm, length: 172mm.
WEIGHT: 260gm (without batteries)

- works with any stone, loose or mounted in jewellery, even uncut stones
- retractable probe tip ensures constant pressure between probe and gemstone
- industry's thinnest probe tip (0.6mm) for testing gemstones as small as 0.02ct
- no waiting time between tests
- operating range 18 to 27 degrees C.
- includes strong nylon carrying pouch, instruction book, extra charts of gemstone readings, batteries, mains power adaptor.

Thermal meter (the analogue meter) does exactly the same as model gemtest-P, Place the probe on the stone to operate the. Click on the picture to see the scale on the meter enlarged; click here to see a more detailed chart of which stones it tests and how the various readings overlap.

The only condition is that the tester and the stones must be approximately room temperature.

WHAT'S NEW? This new model features a totally different method of calibration. Metal alert buzzer to ensure that probe tip is in contact with gemstone during testing.

Reflectivity meter (the digital display) 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).

WHAT'S NEW? A basic chart of readings is built into the tester.


The readings on the thermal tester (the analogue meter) change with temperature, and they also change over time, so you must 'adjust' (calibrate) the electronics every now and again.

With the previous model the process was so complicated that we recommended you sent the entire tester back to us. With this new model calibration is simple and takes just 70 seconds.

For the best results the tester (and the stones) should be at the recommended temperature of between 18 and 27 degrees Celsius. Even at the recommended temperature it is good practise to check the readings against the two discs (built into the tester) before every test, to check that the readings aren't too low or too high.

If it's cool (approx. 15 to 18 degrees) the readings might be a little too high, calibrate the tester.
If it's cold (approx. under 15 degrees) the tester might still work, but it might not, it is designed to work at the recommended temperature.

If it's hot (approx. 27 to 30 degrees) the readings might be a little too low, calibrate the tester.
If it's very hot (approx. over 30 degrees) the tester might still work, but it might not, it is designed to work at recommended temperature.


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.