CONTENTS

TECHNICAL TERMS
COMPARISON CHART FOR ALL TESTERS
TYPES OF TECHNOLOGY

TECHNICAL TERMS

Understand what it is that you're testing

It is important to know what you might be testing. Diamond can be natural (mined) or synthetic (grown in a laboratory, manmade) - they are both real diamond. Moissanite is a purely synthetic (manmade) stone. Simulant means it looks like diamond (or maybe Moissanite) but isn't, it's something else.  

COMPARISON CHART FOR ALL TESTERS

Including: Diamond (Natural & Synthetic),  Moissanite, Ruby, Sapphire and other gemstones

This is our 'master chart' of the features of every diamond and gem tester. If you find it a bit confusing, scroll to the bottom to see a list of the different types of technology the testers use, each has its advantages and disadvantages, decide which type you like, then scroll back up to here and see the "Technology" column. 

Model/Price	Technology See below this chart for a brief explanation	Tests  mounted  stones [1]	Tests  Diamond	Tests  Moissanite	Can tell natural diamond from synthetic diamond	Other stones
Diamond selector II  Under £20. Works some of the time.	Thermal conductivity See article about diamond testing for a detailed explanation	✔	✔	Shows up as diamond	✘	✘
Diamond selector II Under £30. Works most of the time.	Thermal conductivity See article about diamond testing for a detailed explanation	✔	✔	Shows up as diamond	✘	✘
Diamond Experior  Under £100. Best of the 'basic' diamond testers	Thermal conductivity See article about diamond testing for a detailed explanation	✔	✔	Shows up as diamond	✘	✘
Moissanite tester by GemVue Under £100. For Moissanite only.	Electrical conductivity See article about diamond testing for a detailed explanation	✔	✘	✔	✘	✘
Multi-Experior by GemTrue About £200. The most popular.	Thermal conductivity and electrical conductivity all-in-1 See article about diamond testing for a detailed explanation	✔	✔	✔	✘	✘
SAM multi-tester by Presidium About £350. Best quality.	Thermal conductivity and electrical conductivity all-in-1 See article about diamond testing for a detailed explanation	✔	✔	✔	✘	✘
Ari by Presidium £1200.00	UV  absorption See article about diamond testing for a detailed explanation	✔	✔	✔	✔	✘
Arete  by Gemtrue £1000.00	UV  absorption See article about diamond testing for a detailed explanation	✔	✔	✔	✔	✘
Oti by Presidium £1500.00	UV  absorption and thermal conductivity See article about diamond testing for a detailed explanation	✔	✔	✔	✔	✘
Handheld presidium gem tester About £300 Names of stones display on screen, easiest.	Thermal conductivity See limitations	✔	✔	Shows up as diamond	✔	31 stones
Standard Presidium gemtester Under £300 Analogue meter points to the most likely stones.	Thermal conductivity See article about diamond testing for a detailed explanation	✔	✔	Shows up as diamond	✔	17 stones
Presidium Duo gem tester About £400. Analogue meter + digital readout, the most versatile.	Thermal conductivity  and also RI / reflectivity	[2]	✔	✔	✔	[3]
Digital refractometer by Presidium  RI	RI / reflectivity (digital readout)	✘	✔	✔	✔	55 stones
Refractometer (optical not electronic) RI	Optical, look through viewfinder at a scale	✘	✘	✘	✔	Hundreds of stones [4]

[1] All testers test loose stones but not all can test mounted (set in jewellery) stones.

[2] The probe / analogue meter will test mounted stones, the digital meter will only test loose stones.

[3] The probe / analogue meter: 17 stones; the digital meter: 40 stones.

[4] Skill and practice is required to use an optical refractometer, instructions are not included, these are for professional gemmologists.  .

TYPES OF TECHNOLOGY

For more about testing diamond/Moissanite mounted in jewellery, see the article Guide to buying and testing diamonds.

There are four types of technology used for electronic diamond testers. Each has some basic limitations and knowing these will help you choose a tester. 

Q. "Do I really need to know this?"
A. No, but it helps. It's like buying a car, do you really need to know if it's electric, hybrid, petrol or diesel? Possibly not. But it is very basic to what you are buying.  For instance, buying the cheapest (thermal conductivity) tester without realising that it can't distinguish diamond from synthetic Moissanite - that's like buying an electric vehicle without realising you need a charging-point.  

1) Thermal conductivity. Works on temperature. They do not work in extremes of heat or cold, the cheaper models only work at room temperature. Cannot distinguish between diamond and Moissanite. Useful to see if a stone definitely isn't diamond and definitely isn't Moissanite, otherwise of little use. HOWEVER, if you are using the very latest tester (uv-absorption, about £1000.00) you will need one of these 

2) Electrical conductivity. Until recently all Moissanites were conductive and most (98%) of natural diamonds were not. So this was an easy test. But now they are manufacturing Moissanites that are only very slightly conductive. This isn't a problem for recently-made testers, they are tweaked to be more sensitive to detect that 'very slight' conductivity, but older testers (more than a year or two old) will now give false readings. Also, it's not just Moissanite that is very slightly conductive, so too is synthetic diamond. Therefore, a positive test now means the stone is either Moissanite or synthetic diamond (or the 2% of natural diamonds that are conductive).  It is likely that very soon these testers will not be able to tell the difference between moissanite and diamond at all.

Combined thermal/electrical conductivity.  The better testers use both of the above methods, the electronics carry out the thermal conductivity test then, less than a second later, carry out the electrical conductivity test. The best models are also fine-tuned to test for sapphire and ruby. Price range £200.00 to £350.00.  It is likely that very soon these testers will not be able to tell the difference between moissanite and diamond at all.

3) UV Absorption. Can distinguish between natural diamond, synthetic diamond and Moissanite (within certain limits of colour, cut and size of stone). However, you must be certain you are testing a diamond (or maybe Moissanite) by testing the stone on a good quality thermal tester first. Cost: Arete £995.00 incl. VAT (with the option of adding a thermal Diamond Experior for half price = total £1037.00).  

Combined UV Absorption and thermal conductivity. This will test for diamond (both natural and synthetic), and also Moissanite and other simulants. OTi £1495.00.

4) RI, refractive index (technically, these electronic testers are reflectivity meters). FOR LOOSE STONES ONLY (will not test stones mounted in jewellery). You place the  stone over a sensor, the results will indicate many different stones, and it will distinguish diamond from Moissanite. From £279.00.

THERE ARE ALSO MANY OPTICAL TESTERS though these are more difficult to use and are designed for gemmologists. Polariscope, for loose stones (or mounted stones with difficulty). If the stone registers as diamond on the simplest of diamond testers but gives a positive reading on the polariscope then the stone cannot possibly be diamond (it might  be Moissanite but it can't possibly be diamond, which is all you need to know). There's a small battery model eg for a ring (£37.50) or a large mains model for large items (£150.00). Refractometer, the standard tester for gemmologists, more versatile than the electronic version  for testing gemstones but cannot test diamond because diamond is out of range. 

For more about testing diamond/Moissanite mounted in jewellery, see the article Guide to buying and testing diamonds.