Several models reviewed

At the bottom of this page is a list of related articles

(also downloads, includes instruction manuals)



Electronic gem testers

Optical gem testers

Diamond / Moissanite testers



Electronic gem testers - pros and cons

Electronic gem testers - which one?

Related articles

- you must read this before buying an electronic gem tester
(whether you buy it from us or anyone else!)

There is no machine that will simply light up with the name of a gemstone; there is no machine that will distinguish natural stones (grown in the ground by nature) from synthetic (grown in the laboratory by man, using the same chemicals and the same conditions found in nature) – not to be confused with imitations, where one stone imitates another. Gem testers merely suggest possibilities and you must use a combination of experience and other tests to come to a conclusion. Too complicated? Then do not buy a gem tester! Sounds interesting? Then you are about to discover a fascinating world of optics, chemistry, and how to become a super-detective in the quest to identify gemstones.

You may return any gemtester bought by mail if you are not satisfied, providing this is done within two weeks (for new items..all the items on this page are new) or one week (for secondhand items). SETS OF SAMPLE STONES MAY NOT BE RETURNED.

A thermal meter shows several common gemstones (see the picture of the meter below). It is easy to use on both loose stones and stones mounted in jewellery. It cannot distinguish diamond from Moissanite (a man-made stone). It is best for suggesting what a stone isn't e.g. it might be glass but it can’t possibly be sapphire.
A reflectivity meter
is relatively easy to use: the stone must be faceted, with a perfectly clean perfectly polished flat surface that will cover the sensor; you should, ideally, take a few readings to make sure they are consistent. These will will test loose stones, and also stones mounted in jewellery providing they have a perfectly polished flat surface that will cover the sensor. The advantage of reflectivity is that it helps identify dozens of stones.

Gemtester meter

To buy electronic gem testers click here

Some examples of where these testers are of most use:

- you have been given a parcel of stones and want to sort those that are 'interesting' and worthy of further investigation from those that can be put to one side for the moment.
- your supplier of new jewellery has sent you ten sapphire rings and you want to check that they are all the same.
- you have been offered an antique ring described as aquamarine, how likely is this?
- you are in dispute regarding a stone that you know for certain is not diamond (because you have a diamond tester), it looks like diamond but it is an imitation - what is it?
- you know, from your experience, that a customer is offering you paste, he says it's white sapphire, you need to show him the result on a machine, because people tend to believe machines.

Some examples of where these testers are of least use:

- you are quite happy to work slowly and carefully in laboratory-clean conditions, but you must have a machine that will positively identify any stone.
- OK, you understand the limitations of gem testers and that's fine, but there really is no way you have time to keep the tester meticulously clean and clean every stone before every test, and you cannot guarantee that it will never be bumped or dropped or get dusty or damp.

Here are some independent evaluations from two internet forums run by gemmologists. Gemmologists are scientists, they are not interested in sales hype:

Just this morning some students and me have been checking the digital refractometer. In this case we tried to find out if a stone purchased on internet was indeed a GGG or a CZ. This reflectivity meter worked (in this case). The result was proven by its SG.

[the Presidium Duo] is good for quick sampling, but you do need to keep it calibrated with known samples. I also haven't been able to get it to work reliably with tiny stones. Relying on any one characteristic to identify a material practically guarantees misidentification.
- Used in combination with other tests I find this tool quite vital and use it daily!
- I use it for doing those quick IDs that have two possibilities and need a quick decision on which one it is, works perfectly
- An approximate reading obtained quickly and neatly is very useful in confirming ID in many parcels. Spinel parcels often need the garnet weeded out, Tsavorite parcels need the chrome tourmaline weeded out, and so on. Seems like this may be a time saving instrument on checking parcels of many varieties.



Standard Presidium (thermal conductivity) £195.00

Presidium Gem Tester

- this is by far the easiest tester to use, you don't need to clean the stones or take a few readings, you don't need to look up charts.
- confirms what you already know; for instance, your supplier is reliable and describes the stone as ruby, the machine shows it might be ruby, it's probably ruby.
- tells you what a stone is NOT. For instance, you will easily see that a stone might be glass, garnet or tourmaline, but that it can't possibly be topaz, ruby or sapphire.
- it's remarkably good value for a machine of this sophistication.

- as you see from the picture of the scale at the top of this page, it lists only a handful of stones, and many of the readings overlap.
- I do not recommend you use this as a 'diamond tester', the diamond zone of the scale does not distinguish diamond from Moissanite

Duo Presidium (thermal conductivity and reflectivity) £289.00

Presidium Duo Tester

The 'thermal' part of the tester (with the scale that shows the names of the stones) is identical to the standard model, above, so see above for pros and cons.

In addition, it has a reflectivity meter. This gives the result as a number which you look up on a chart. The chart includes 76 common gemstones, and we include two versions of the same chart, the first in numerical order (so you can look up the reading), the second in alphabetical order of gemstone (so if you already have a good idea as to what the stone is, you can see how closely the reading on the machine matches it).

Advantages of the reflectivity meter:
- to sort parcels of stones to see which look 'interesting' and worthy of further investigation
- to confirm stones are as described by your supplier
- to identify diamond simulants (you will need the set of sample stones)
- to show a customer the reading, when you already know what the stone is and just need to 'prove' it
- to narrow the possibilities so that you can carry out further investigations

Disadvantages of the reflectivity meter:
- the stone must be faceted, with a perfectly polished flat surface that will cover the sensor
- you must work slowly and carefully and everything must be spotlessly clean (both stones and sensor).
- you must treat the machine as a very sensitive piece of laboratory equipment - be gentle, keep it clean.
- if you want to test high-refractive stones (most stones used to imitate diamond) you will need the set of samples so that you can accurately compare the readings on the machine with actual stones. It helps greatly if you can collect samples of other stones, comparing the reading with a real stone is better than just relying on a number on a display.
- instructions are minimal. We have managed to obtain extra instructions and charts that are not normally included, but you will still have to be patient whilst learning how to use this.


Digital Refractometer £329.00

All the pros and cons of a the reflectivity meter in the Duo, above, apply to the digital refractometer too. But there is one big difference. The number it displays is refractive index, the standard number every gemmologist understands, the number you can look up on any standard reference chart, the number that will help identify many hundreds of gemstones.

Easy to use, and the result is displayed within one second. The only condition (as with all these machines) is that the stone must have a perfectly polished flat surface that covers the sensor. That includes stones mounted in jewellery (unless the item -cut stones (they're not flat) and not stones in large and lumpy jewellery that won't fit.

As I have said many times above, there is no machine that will simply 'positively identify' any gemstone - but if you are serious about being able to identify hundreds of gemstones, this is by far the best and, in my opinion, well-worth the extra money.



The complete guide to testing diamonds

Distinguishing diamond from Moissanite

Diamond tester trouble shooting

A little about optical gem testers


See also: all articles on this website or latest articles on this website