How-To: GemVue Diamond Tester

Published: February 2013

The JEM-II GemVue™ Diamond Tester accurately measures the thermal conductivity of the gemstone to determine whether it is a diamond or a diamond stimulant. This diamond tester WILL NOT identify synthetic Moissanite which has a similar thermal conductivity to a diamond.

The JEM-II is equipped with a metal alert, designed to reduce the possibility of a false positive reading caused by touching the metal holding the stone. Easy calibration with the level meter volume to match different size stones and can distinguish stones as small as 0.2ct. Can be connected with an A/C adapter for long time indoor use, but NOT INCLUDED. This model is also equipped with an ultraviolet light to test fluorescent reaction of stones.

Use this durable diamond tester at home, in the office, or on the road.

This item complements several other items in our line of Jewelry Television® gemstone and jewelry making tools and equipment.

Preparing to Use the Diamond Tester:

1. Slide open the battery cover in the direction of the arrow.
2. Insert the 9V battery.
3. Slide the power switch until it reaches the Diamond selection.
4. The power bulb will turn a solid red and the adjacent ready bulb will blink green.
5. Wait about 30 seconds for testing probe to heat up.
6. Once the ready bulb flashes a solid green and makes a very short beep the power up cycle is complete.
7. Please make sure the LED level meter is lighted up to the second column (if not, please adjust the volume control until the bar light is at the second column), now you can begin testing.

JEM-II diamond tester


Always properly clean the stone before testing
Gently remove the protective cap from the probe tip.
Hold the diamond tester in your right hand, with your index finger touching the electricity-conducting panel on the top of the diamond tester.
Press the probe tip at a right angle (see example) onto the top of the stone. Do not press the tester to a stone at an angle less than 90 degree.
CAUTION: Too much force may break or bend the probe tip!
When testing stones that are already mounted, hold settings with your left hand.
For loose stones, best results occur when the stone is placed in the testing base. Secure testing base with one hand.


Interpreting the Results of the Test:

If LED lights up to the red zone with three periodic bees, the stone being tested is a diamond.
If LED lights up only to the green and/or yellow zone, then the stone is a stimulate or non-diamond.
If the probe tip comes into contact with metal, the diamond tester will emit a continuous beep.
The recommended testing temperatures are between 64 °F - 86 °F.
When testing small stone (0.5ct and below) it is recommended that you remove them from their settings to let them cool down to room temperature and then place them in the testing base for proper testing. Also when testing small stone (0.5 ct. and below) the volume control will have to be increased to the third bar to ensure accurate readings.
The JEM-II emits audible and visual signals. Refer to the table below to interpret those signals.
Wait for the READY light to be a solid green between each test.

This Signal Indicates This Result

1. Beeping sound (beep-beep-beep): Diamond
2. One or more red bars on level meter box light up (the bigger the stone, the more red bars light up): Diamond
3. No beeping sound: Diamond Simulant
4. No red bars illuminate: Diamond Simulant
5. Continuous buzzing sound: Metal Alert (Disengage, the probe tip, then re-touch only the stone.)

diamond tester pressed against gem

Using the Ultraviolet Light

Before you start to use the ultraviolet light, we want to stress that ultraviolet light can be dangerous if used carelessly.

The information provided by the ultraviolet lamp can be an important clue in gem identification. It will immediately show you whether or not the stone fluoresces or phosphoresces. While it is seldom a conclusive test, it can be a fast and easy way to confirm you diagnosis when used in conjunction with other tests.

Here are a few rules to follow when using the ultraviolet light:

Never look directly into the ultraviolet light.
Avoid continuous exposure of the ultraviolet light to your skin.
Do not turn on the UV lamp until everything is in proper position for testing.
Whenever possible, use protective goggles or glasses.
Clean both the stone and/or the mounting in which the stone may be set.
Make sure you are in a non-reflective darkened environment. The darker the environment the better results.

Testing Procedure:

Hold the lamp directly over the item being examined, WITHOUT TURNING THE UV LAMP ON.
Place the UV lamp as close to the stone as possible. The closer the stone is to the lamp, the easier it will be to see any type of reaction to the UV radiation.
NOW, turn the lamp on.
View the stone from several different directions for best results.
Turn off UV lamp.

Additional Instructions:

The diamond tester is designed to detect normal moisture level in the users hand, so if the skin is very dry or the user wears gloves, it will not function properly.
When testing stones set in a metal setting, hold in the setting in your left hand.
When testing loose stones, place the tested stone on the metal testing platform. Hold the tester in your right hand and the testing platform in your left hand.
Repeatedly testing the same stone will heat the stone until a natural diamond will no longer read DIAMOND. If this happens, wait at least three minutes for the stone to cool down.
After use, always turn off the diamond tester and store in its case.
Avoid exposing the tester to dust and humidity. Because the tester contains precise electrical circuits, never attempt to open anything except the lid of the battery compartment.

ultraviolet diamond tester close up


If the diamond tester is not going to be used for an extended amount of time, the batteries should be removed from the tester.
ALWAYS place the testing probe protective cover on the JEM-II when not in use.
In case red light becomes dim, please replace the battery at once.


JEM-II uses a 9 volt battery or an AC adapter (not included) 110V-240V
Probe warm up time is around 30 seconds.
Working time: about 5 hours of continuous use.
Working temperature: 64°F - 86°F

diamond tester gauge close up