How to use a diamond tester?

A diamond tester checks whether a stone behaves like a diamond by measuring thermal conductivity, electrical conductivity, or both.

To use it, clean the stone, let the tester calibrate, place the probe on the diamond, and wait for a reading.

The result is only a clue—not a final answer.

Basic thermal testers can confuse diamond with moissanite. Combination testers reduce that risk, but no handheld tester can confirm whether a diamond is natural or lab-grown.

At Ganem Jewelers, we treat testers as a starting point, not a conclusion.

What Does A Diamond Tester Actually Test?

Most testers measure how fast a stone conducts heat.

Diamonds conduct heat very quickly. Glass, cubic zirconia, and other simulants do not, so they are usually easy to separate.

Some testers also measure electrical conductivity. This helps distinguish diamond from moissanite, which can sometimes pass a thermal-only test.

What A Diamond Tester Can And Cannot Tell You

Gem Fact

Natural and lab-grown diamonds test the same on basic devices.

How To Use A Diamond Tester Step By Step

Always follow your specific model’s instructions first. These are the general steps.

1. Clean And Dry The Stone

• Dirt, oil, or moisture can affect the reading.

• Wipe the stone and make sure it is fully dry before testing.

Even a thin film can cause inconsistent results.

2. Turn On And Calibrate

• Let the tester warm up if required.

• Some models need calibration before use.

Skipping this step can lead to false readings.

3. Stabilize The Jewelry

• Place the ring or stone on a flat surface.

• Make sure the probe will touch only the stone, not the metal.

This is especially important with small mounted diamonds.

4. Place The Probe Correctly

• Touch the probe gently to the diamond’s surface, ideally the flat top (table).

• Keep the tester steady and straight.

Do not press hard—contact matters more than pressure.

5. Read And Repeat

• Results may appear as lights, numbers, or sound alerts.

• Test more than once if possible.

One reading is not enough to confirm anything.

Expert Tip

If results change between tests, stop and get a professional evaluation.

Why Does My Diamond Tester Say Moissanite?

This usually happens with thermal-only testers.

Moissanite conducts heat similarly to diamond, so it can trigger a “diamond” reading.

Multi-testers that also measure electrical conductivity are more accurate.

This is common with older jewelry or secondhand pieces.

Do not assume the tester is broken—assume more testing is needed.

Can You Test A Diamond In A Ring?

Yes, but accuracy depends on access.

The probe must touch the stone, not the metal.

Watch The Prongs

Small diamonds are easy to misread if the probe touches a prong.

Small Stones Are Harder

Pavé, halo, and channel-set diamonds are difficult to test individually.

Do not loosen stones at home. A jeweler can test them safely.

From The Jeweler’s Bench

The more complex the setting, the less reliable handheld testing becomes.

Why A Real Diamond Might Test Wrong

A false result does not mean the stone is fake.

Common causes include:

• Dirt or oil on the stone

• Moisture

• Poor probe contact

• Touching metal instead of stone

• Very small diamond size

• Temperature changes

• Low battery

• Poor calibration

Clean, recalibrate, and retest before drawing conclusions.

If results stay unclear, stop and seek professional testing.

Can A Tester Tell Natural From Lab-Grown?

No.

Both are real diamonds with the same basic structure.

They test the same on handheld devices.

Only advanced equipment or lab analysis can determine origin.

If origin matters, documentation and professional screening are essential.

When Is A Home Diamond Tester Useful?

A tester is best for quick screening, not final answers.

It helps when:

• Sorting loose stones

• Checking inherited jewelry

• Identifying obvious simulants

• Getting a first impression

It is less useful when:

• Stones are very small

• Settings block access

• You need origin verification

• You need value or appraisal

• The jewelry is high-value or sentimental

What To Do After Testing

If results are consistent and expected, you may be done.

If the jewelry has financial or emotional importance, go further.

A professional evaluation can confirm:

• Whether it is a diamond

• Natural vs lab-grown (when possible)

• Condition and wear

• Setting security

• Treatments or issues

• Whether lab testing is needed

Our Perspective At Ganem Jewelers

We often see jewelry with no paperwork and unclear history.

A tester gives one quick data point.

But experience, magnification, and proper tools give the real answer.

The important question is not just, “Did it test as diamond?”

It is, “What is this piece, and what should you do with it?”

Use A Diamond Tester As A Starting Point

To use a tester correctly: clean the stone, calibrate the device, test carefully on the diamond only, and repeat the reading.

Do not rely on a single result.

A tester can separate diamond from many simulants, but it cannot determine value, quality, or origin.

If the jewelry matters, professional evaluation is the next step.

At Ganem Jewelers in Scottsdale and Ahwatukee, we can help you understand, evaluate, and care for your diamonds before you decide what to do next.