Best Diamond Testers: Which One Should You Use?

When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn more.

Choosing a diamond tester is an easy task. Which one you opt for depends on what you want to use it for. Do you want a simple ‘yes’ or ‘no? Do you want to test small diamonds? What about the option to test for other gemstones too?

Let’s take a look

What are the best diamond testers to buy

What are the best diamond testers to buy?

There are 3 different types of diamond testers available to buy, electricity, heat or combo testers.

In my personal opinion and from extensive research the combination diamond testers are the best. This is because they also allow you to test if the stone is moissanite.

1. KKMoon Diamond Selector II V2 – Cheapest Diamond Tester Pen


  • LED lights and tone audio results.
  • Easy calibration for stones of various sizes.
  • Reliable and accurate testing.
  • Includes carry case.
  • Lightweight design with tough plastic housing.
  • Matched with a testing platform for loose stones.


The cheapest of diamond detectors is the Diamond Selector II. It comes in at a very budget price and is well received by customers with many positive reviews.

Perhaps not the most well-built diamond tester, although this a great choice for general use, I wouldn’t recommend it for a jeweller who is relying on the accuracy in a shop or when buying and selling.

Very simple to use and comes with its very own carry case. The display is very easy to interpret and uses both LED and sound to alert you of whether you have a real diamond or not.

Highly recommended for those who just want to perform tests on diamonds casually, but I really don’t believe this is good enough for professional use.

That being said at this price and with this many positive reviews, it really is a bargain!

2. Presidium DiamondMate-C Electronic Tester – Most accurate Diamond Detector


  • Low battery consumption and low battery indication ensure the tester is always with power.
  • Uses the latest technology and thermal conductivity to detect and test for diamonds and simulants.
  • Metal detector function will alert the user when contact has been made with the gem mounting and not the stone.
  • Instant recovery time in between tests with no wait.
  • 1 Year Manufacturers Warranty


Delving into the more professional range of diamond detectors Presidium is one of the leading brands.

The Presidium DiamondMate-C is a quality, well constructed durable piece of kit that uses the latest tech and thermal properties to run its accurate and stable tests.

Results are given instantly and this Presidium diamond detector pen has one of the thinnest pin probes you will find in the industry allowing you to test very small diamonds.

It features a rechargeable battery which can be charged via USB lead and will also tell you if you are making contact with the mount and not the stone when performing the tests.

Presidium is a Jewellers main choice and the DiamondMate-C can be found in many Jewellery stores nationwide.

A great bit of kit, very accurate and highly recommended if you are serious about testing diamonds.

3. Presidium Refractive Index Meter II PRIM II – Best Diamond Tester


  • Pinhole Light reflectivity measure on a wide oval-shaped platform.
  • Cover cup included with a blackout interior to make sure the light reflectivity measurement is correct.
  • When testing it will instantly display a direct R.I reading on the digital LED display panel index.
  • In-built Refractive Chart for referencing diamonds and simulants above R.I reading of 1.8
  • 8 Piece Gem Stone Holder built-in.
  • Pocket-sized Refractive Index Chart R.I readings for 55 types of stone.
  • PRIM II PC  software to help users find out further information on the possible coloured gemstone using extensive data on the various gemstone properties.
  • Gemstone Dictionary with 57 gemstones’ properties (R.I, Color, Hardness, S.G. Value), country of origin and other related information.
  • USB port for alternative power source and connectivity.


The PRIM II is one of the most advanced diamond testers available on the market, it uses refractive light technology and is one of the only diamond detectors that are able to easily determine the difference between diamond and moissanite. It can also test many other gemstones.

It features a clear LCD screen which displays the results of the refractive light test, you can then compare the results to the scales shown on the decal allowing you to determine what stone you have.

Presidiums refractive index meter also has an extensive CD library for your PC allowing you to further identify all kinds of gemstones. If you are going to be testing diamonds regularly then I stand by the fact that this is one of and if not the best you can buy.

It’s lightweight, compact and well built and can either run on batteries or via the AC adaptor.

Detector Reviews number one choice!

What is a diamond tester?

Diamond testers are electronic devices, more often than not, in the shape of a handheld device called a diamond testing pen.

The device has a needle tip that is placed on the stone that needs to be tested. If you have a real diamond the diamond detector will show you via its LED display or by making a beep sound.

How does a diamond detector work?

Diamond testers work on the principle that gemstones and diamonds each conduct a different amount of heat. Heat will travel through a diamond differently than it would a glass stone, cubic zirconia or moissanite. Moissanite is the only stone that the detectors will perhaps struggle with as the heat travels through moissanite at a similar rate as diamond.

The diamond detectors will test the speed of the heat travelling through the stone and then give you a readout as to whether it is a real diamond or not.

There are other kinds of diamond testing equipment, the diamond pens use the heat principle whereas some others use an electric pulse or refractive light.

Do diamond testers really work?

Yes! Diamond testers really do work and many jewellers will confirm this. They are perhaps the most reliable test you can perform to authenticate the diamond. As previously mentioned the diamond testing pens that use heat can mistake diamonds for moissanite stones.

In this instance that the diamond detector can’t determine between the two you can perform the test using a diamond detector that uses electricity to test authenticity.

There are now models that combine both heat and electricity to test making it very accurate, these are a little more expensive but well worth the extra money.

Available also for gemstone testing are refractive light devices, these use refractive light to determine the type of stone.

How do you use a diamond tester?

Using a diamond tester could not be more simple.

  • First, you will need to clean the stone you are about to test, gently wipe away any dirt or residue.
  • Remove the cap from the diamond testing pen to expose the needle tip
  • In your right hand, you will now hold the diamond tester, place the suspected diamond into some kind of stable testing base or hold firmly in your left hand.
  • Using the needle tip of the diamond detector push down onto the stone carefully, you need to hold the tip at no less than a 90-degree angle. Try not to press down too hard as this could possibly break the detecting tip.
  • Use the instructions of your diamond tester to determine what the reading means on the LED lights. Most diamond testing pens and testers are different and have their own unique way of displaying the results.

Related Articles