How To Read A Diamond Tester? (Step By Step Guide)

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One of the more reliable methods of testing for diamonds is to use the diamond tester. It is a device that detects and tests for diamonds and the gemstone known and moissanite by testing the gemstone’s thermal and electrical conductivity.

And if you are trying to figure out if the gemstones you are looking at is fake or real, a diamond tester would be the ideal gadget to use.

In this article, we’ll be sharing important insights into what you need to know about diamond testers and how to use them.

So, let’s get right to it!


What is a diamond tester?

A diamond tester can be defined as a small, portable device with a needle-like tip that is used to test the gemstones.

The needle-like tip is placed on the stone to be tested, and if the gemstone being tested is made of real diamonds, then the device would light up or sound a signal to indicate if the stone is genuine or not.


How does the diamond tester work?

The principle of operation for the diamond tester is based on the fact that gemstones have different levels of heat conductivity.

How To Read A Diamond Tester

In the case of diamonds, heat will pass through them in the diamond differently like other seemingly dazzling metals like glass or cubic zirconia, hence the use of diamond testers.

The tester will specify the rate of heat transfer through the stones, telling you if the gemstone is genuine or fake. The diamond testers could also test for the stone’s electrical conductivity, and they work on the same principle, testing for the conductivity of electricity rather than that of heat.

In most cases, the diamond testers are used by the jewelers to determine the authenticity of the diamond jewelry, especially if you take jewelry to the jewelry store with the intention of selling or exchanging it. Just to make sure that the gemstones are real, the diamond tester would be used.


How to read a diamond tester (Step by Step Guide)

Read Diamond Tester

Diamond testers, as mentioned above, will take accurate measurements of the thermal conductivity of the diamonds/ gemstones tested to determine if the diamond is a simulated piece or a genuine diamond.

However, the diamond tester is unable to accurately test for or identify the synthetic stone known as the moissanite because it shares the same thermal conductivity as diamonds.

The diamond tester, for example, the JEM-II, is designed with a metallic alert system which is meant to reduce a fake positive reading that would result from the tester touching the metal, even if the stone is not a diamond or some other kind of gemstone.

How To Read A Diamond Tester

The tester is calibrated for ease of use and accurate readings with the metered volume, which matches stones of different sizes.

It also has the capacity to identify stones that are as small as 0.2ct.

You’d have to connect the tester to an AC adapter for use indoors, but the tester doesn’t come with the AC adapter that is needed. You will be happy to know that given the small size of the tester, you can carry it in your pocket.

Follow the following steps to use the diamond tester.


How to use the diamond tester – Prepping to use the diamond tester

How To Read A Diamond Tester

1. First, slide open the tester’s battery cover in the arrow’s direction, then insert a 9V battery. Then you have to slide the power switch until it gets to the Diamond option – in this position, the power bulb turns a solid red, while the adjacent bulb blinks green. Give it about 20 seconds more to allow the testing probe to heat up fully.

2. You will know that the probe is heated up to the right temperature when the bulb starts to flash a solid green and make a short beep – this means that the probe is ready for use and the power-up cycle is complete.

3. Also, make sure that the LED-level meter lights up in the 2nd column, and if it doesn’t, you’d want to adjust its volume control until the bar light in the second column lights up.


Testing gemstones using the diamond tester

Read Diamond Tester

1. You should always clean the tester and the probe thoroughly before you use them.

2. When ready to use the tester, remove its protective cap gently from the probe tip.

3. Next, hold up the diamond tester with your right hand’s index finger so that you touch its electricity-conducting panel on top of the diamond tester.

4. You’d want to press down the probe’s tip at the right angle on the stone. Just make sure not to press the tester on the stone at less than 90 degrees. Also, don’t apply too much force because it may bend or break the probe.

5. Once you’re ready to test, hold the testing probe settings with the left hand.

6. If you are testing for the loose stones, you should place them in the testing base – you can use one hand to secure the base.


How to interpret the test results

I. If the LED lights up on the red zone, producing three beeps, it means that the stone you are testing is an actual diamond.

But if it only lights up all the way to the green or/and the yellow zone, then it means that the stone is not a diamond or, at the very least, a simulated diamond.  (Watch the video below)very easy!

II. Note that if the probe tip is in contact with a metal, the tester will produce a continuous beep.

III. Generally, the recommended testing temperature for diamonds is between 64 and -84 degrees Fahrenheit.

IV. If you are testing a small stone that is below 0.5ct, you may want to remove the tester from its settings to allow the probe to cool down before you use the tester again. Also, you want to use the volume control at the third bar to ensure more accurate readings.

V. The visual and audio signals emitted by the tester will tell you everything you need to know about the nature of the test material.


Still unsure about what you should be looking for when using the tester, here is what you should know:

How To Read A Diamond Tester

  • A beeping sound (3 beeps) means that the test stone is a diamond
  • At least one red bar on the meter level for bigger stones means diamonds – especially when many red bars light up.
  • If there is no beeping sound – the test material is a simulated diamond. This is also true if there are no red bars that illuminate
  • In case of continuous buzzing, then you’d be testing a metal, or the probe tip is in contact with metal, and you’d want to disengage the tip them move it to the stone.
  • And if you’re testing sapphires or rubies, the detector will go all the way to 8 on the volume level.


Other important considerations to keep in mind when it comes to diamond testers

How To Read A Diamond Tester

It’s important to note that your diamond tester is made to also detect the moisture levels on your hands, and it won’t work too well if you have a glove on or if your hand/ skin is too dry.

If you are testing stone jewelry that is set on a metal setting, you’d want to hold the jewelry in the left hand.

You should also know that when you test the same stone too many times, the stone will be heated up, and the results on the tester will tell you that the diamond is not a diamond even when it is. So, you shouldn’t test the stone too many times, and if it heats up, allow it to cool for about 3 minutes.

When done testing the diamonds, turn off the tester, and put it back in the case for storage. To ensure the best use of the tester in the long term, don’t expose the tester to humidity or dust because it has high-precision electrical circuits that would be damaged by the elements. Also, you should never open the other parts of the tester unless it is the battery compartment.



Not sure if the ring you recently purchased is made of diamonds or diamond simulants, the diamond tester might be a great option for you. Follow the steps above to test the diamond jewelry with ease and a high level of accuracy.

Read more useful tips here or here!

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