My Experience with Presidium Duo Tester - Gem Testing

Presidium Duo Tester is an interesting gem testing equipment. I have two of them and have been using them for over five years for testing gemstones. Originally, I bought them as a convenient substitute for the refractometer to take on the field when I go to purchase gems in open gem markets where I don't have the convenience to use a refractometer. Since there is no liquid to use, in my opinion, Presidium Tester makes it a convenient tool on the go for gem testing.

for those who are new to this tool, there are two types of testers namely, Presidium Tester and Presidium Duo Tester. Presidium Tester has the thermal sensitivity test only while the latter has an additional light reflectivity test which is useful in cross checking your test results.
My personal experience is that sometimes, the digital reading of the light reflectivity test for the same type of stones can be a few digits off from stone to stone. If the table of the stones you are checking are small, has an uneven checker board type surface or a cabochon, it may not cover the tiny hole on the tester properly giving you inaccurate readings. In such situations it is very useful to have the second thermal sensitivity test to cross check your results.
In order to get the best out of this tester, it is very important to know how the stones you handle day today would react to it. The dial has overlapping markings as to where the needle would be for a particular stone. Once you use a couple of stones of the same type, you know how far the spindle moves on the dial and you can make a mental note of it to check the rest of the stones of the same type. With the knowledge of the other properties of the gemstones you deal with such as color variations, inclusions that are typical to them and hardness, these tests can give you a great input in making the correct identification.

To give you few examples from my own experience, I have an easy way to separate topaz from quartz using this tester because the thermal sensitivity reading for those two stones are very far apart even though the two stones look similar. Also, an earth mined zircon gives a light reflectivity reading over 35 up to 50 and a very small movement of needle on thermal sensitivity test where as a tourmaline or a kornerupine which can be easily confused as a zircon gives a light reflectivity reading in a range of 20-30 and a much higher needle movement on the thermal sensitivity test. So, it is very important to know how the stones you normally deal with behave in these tests. Along with the other general knowledge you have about your gemstones, in my opinion, Presidium Duo Tester can be an invaluable tool.
I look forward to add more information and pictures on this article. You can check out my okay store for natural gemstones.