Diamond tester and gem tester comparison chart

CONTENTS

TERMS
(Understand what it is that you're testing)

TYPES OF TECHNOLOGY
(Know what each type of tester can, and can't, do)

COMPARISON CHART OF MODELS - FOR DIAMOND, MOISSANITE, RUBY/SAPPHIRE
COMPARISON CHART OF MODELS - FOR NATURAL DIAMOND V. SYNTHETIC DIAMOND

 

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. Sapphire and ruby can be either natural or synthetic.  

TYPES OF TECHNOLOGY
(Know what each type of tester can, and can't, do)

There are five types of technology used for 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. 

Thermal conductivity. Works on temperature. They do not work in extremes of heat or cold, the cheaper models only work at room temperature. These cannot distinguish between diamond and Moissanite. Cheap (from £17.50 to £82.50), OK if all you need to know is that a stone definitely isn't diamond and definitely isn't Moissanite, otherwise of limited use.

Electrical conductivity. 2% of natural diamonds are electrically conductive (98% are not). Until recently all Moissanites were conductive. So this was an easy test. But now they are manufacturing Moissanites that are very slightly conductive. This isn't a problem for recent testers, they are made more sensitive to detect that 'very slight' conductivity. However synthetic diamond is very slightly conductive too. Therefore, a positive test now means the stone is either Moissanite or synthetic diamond (or a 2% chance that it's a natural diamond). 

(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. They cost between £200.00 and £350.00).

UV fluorescence. 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) since it can give false readings on other stones. Do not confuse this with the UV light on many electrical-conductivity testers, that is just to help make Moissanite testing more accurate. Cost: about £1000.00.

(With the Arete (UV) we offer a Diamond Experior (thermal) for half price. This is by far the cheapest way to 'reliably' test diamonds. These two technologies will soon be available built into one tester. 

RI, refractive index (technically, the electronic testers are reflectivity meters). You place a loose stone over a sensor, the results will indicate many different stones (see chart below) and it will distinguish diamond from Moissanite. But it only works with loose stones, not stones mounted in jewellery. From £279.00.

Polariscope. This is an optical device (not electronic), easy for loose stones, a bit fiddly for mounted stones. If the stone registers as diamond on the simplest of diamond testers and you get a positive reading on the polariscope then the stone cannot possibly be diamond (it might not 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).
 

COMPARISON CHART OF MODELS - FOR DIAMOND, MOISSANITE, RUBY/SAPPHIRE

Model / technology

Tests mounted stones [1]

Tests  Diamond

Tests  Moissanite

Tests
Ruby / 
Sapphire

Other stones

Diamond selector II (works some of the time)

Thermal

Shows up as diamond

Diamond selector II

(cheap but works most of the time)

Thermal

Shows up as diamond

 ✘

Diamond Experior 

(best thermal) 

Thermal 

Shows up as diamond

Moissanite tester by GemVue

Electrical

You must only test stones you are certain are diamond or Moisssanite

Multi-Experior by GemTrue

(most popular)

Thermal and
Electrical

SAM multi-tester by Presidium

(Best)

Thermal and electrical

Ultratester 3+ by Gemoro

(new product)

Thermal and electrical

White sapphire

Testerossa by Gemoro

(new product)

Thermal and electrical

White sapphire

Handheld presidium gem tester

(easiest)

Thermal

Shows up as diamond

31 stones

Standard Presidium gemtester

(Basic)

Thermal

Shows up as diamond

17 stones

Presidium Duo gem tester

Thermal and
RI

[2]

[3]

Digital refractometer by Presidium 

RI

55 stones

Refractometer (optical not electronic)

RI

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.  

COMPARISON CHART OF MODELS - FOR NATURAL DIAMOND V. SYNTHETIC DIAMOND

The testers in the chart above test for natural diamond but are not reliable on synthetic diamonds, often showing them to be Moissanite in error. The only way to know is - once you are quite certain that the stone is either diamond or Moissanite, test it on a synthetic-diamond tester:

Model

Approx. price incl. VAT

Tests mounted stones?

Natural diamond

Synthetic diamond

Moissanite

Ari Synthetic Diamond tester by Presidium

£1150.00

Arete Synthetic Diamond tester by Gemtrue £995.00


Natural diamond is mined from the ground; synthetic diamond is grown in a laboratory by man (manmade, lab-created). They are the same.

  • They are the same chemically (carbon)
  • They are the same physically (same crystal structure, hardness, density)
  • They are the same optically (refractive index, reflectivity, dispersion)
  • They are the same visually (the best expert using the best microscope can’t tell them apart)

So far, the only test is to shine an ultra-violet light through the stone and measure the change in light (UV fluorescence).
 
You must be quite certain that you are testing a diamond (or a Moissanite). First test it on a diamond tester, if you don't have one, the good-quality Diamond Experior is available at half price if you buy it with the Arete.