Do Lab Grown Diamonds Pass a Diamond Tester?

One question that is popping up more and more frequently when it comes to the purchase or evaluation of diamonds: Do lab-grown diamonds pass a diamond tester?

It’s a legitimate concern, especially so now that these lab-grown stones are gaining popularity for their eco-friendly mining process and pricing. 

At first glance, lab-grown diamonds are indistinguishable from natural ones. But are they any good when you put them through professional testing tools? Traditional diamond testers work by testing thermal conductivity, which both natural and synthetic diamonds conduct well. That means yes, they typically DO pass standard testers. However, there is more nuance when it comes to distinguishing them from simulants or natural stones using advanced testers.

In this post, we’ll break down how diamond testers work and what that means for lab-created gems.

How Does the Diamond Tester Work in the Lab-Grown Diamond Case?

AdobeStock/LaongdaowDuangkaew

So What’s the Catch?

Lab-grown diamonds can pass almost all common diamond testers, including thermal conductivity devices. Why? Because lab-grown diamonds have the same heat conductivity as natural ones. This means they will trigger the same result on a thermal tester. 

Some diamonds grown with the CVD method might sometimes cause a false positive on multi-testers. This depends a lot on how the device is set up and the overall quality of the tool.

An old tester or one that isn’t built to check for Moissanite or synthetic stones may give you confusing or wrong readings. It happens more often than many people expect.

Different Testers Used to Distinguish Lab Diamonds Accurately

Here are the main types of gemstone testers used today and how effective they work in telling lab-grown diamonds and Moissanite apart:

Tester Type	Accuracy	Does it Work Well	Key Features
Thermal Conductivity Tester	High for confirming diamond presence	✅ Yes	Reveals growth patterns unique to lab-grown diamonds
Electrical Conductivity Tester	Moderate	✅ Yes	Detects trace elements and identifies lab-grown vs. natural diamonds. Moissanite & zirconia, too.
Dual (Thermal + Electrical) Tester	Higher than single testers	✅ Yes	Analyzes crystal growth and surface characteristics
UV Fluorescence Device	Very High	✅ Yes	Screens for Type IIa diamonds (many lab-grown are Type IIa)
Infrared Spectrometer	Extremely High	✅ Yes	Detects CVD and HPHT lab-grown stones quickly
Photoluminescence Spectrometer	Extremely High	✅ Yes	Identifies natural, CVD, and HPHT diamonds with clear reports

Key Limitations and Variables

No matter how advanced, no tester is 100% foolproof in every scenario. Here’s why:

• Mounted stones can skew results due to interference from metal settings.
• Temperature and humidity can affect thermal readings.
• Stone cleanliness plays a role; oils or dust can cause inaccurate readings.
• Some CVD lab-grown diamonds can show minor electrical conductivity, leading to rare but possible misclassification.
  

Therefore, while testers are vital tools, they should be used in conjunction with:

• Visual examination under magnification
• UV or long-wave light inspection
• Professional gemological certification (GIA, IGI, GCAL)

How Do You Test Lab-Grown Diamonds For an Accurate Result?

The Diamond Testing Process enables jewelers and gem experts to become aware of the reality regarding the identity and origin of a diamond. The procedure normally follows the following:

Step 1: Visual Inspection

At the start, the jeweler takes a magnifier to check the stone carefully. They do this step before touching any testing devices. They look for:

• Inclusions (internal features)
• Growth patterns
• Laser inscriptions
• Clues that indicate whether it’s natural or lab-grown

Step 2: Thermal Conductivity Test

A thermal diamond tester is applied to the stone. This device:

• Heats the tip slightly
• Touches the stone’s surface
• Measures how quickly heat travels through

Natural and lab-grown diamonds have high thermal conductivity, so they usually pass this step.

Step 3: Electrical Conductivity Test

To distinguish diamonds and Moissanite, some testers use electrical conductivity. Diamonds are bad conductors of electricity, and Moissanite is a good conductor of electricity.

Step 4: UV Fluorescence Examination

The gemologist also observes the stone's fluorescence using ultraviolet light. Most Lab-grown diamonds exhibit unique fluorescence issues that are not typical of natural diamonds.

Step 5: Advanced Spectroscopy or Imaging

For conclusive identification, labs use advanced tools like:

• DiamondView (De Beers): Reveals growth patterns and fluorescence unique to lab-grown diamonds
• Infrared Spectroscopy: Detects trace elements that point to synthetic origins
• Photoluminescence: Shows patterns in atomic structure

Step 6: Certification and Grading

• If the stone passes all tests, it is graded and documented by reputable organizations such as:
• GIA (Gemological Institute of America)
• IGI (International Gemological Institute)
• GCAL (Gem Certification and Assurance Lab)

Which certification is better for Diamond Quality?

These labs issue a grading report clearly stating whether the diamond is natural or lab-grown.

FAQs

Why Don’t Some Lab-Grown Diamonds Test Like Natural Diamonds?

Some lab-grown diamonds, especially CVD types, can show different conductivity levels that confuse standard testers. Older or basic testers may misread them as non-diamonds. That’s why advanced testing or lab certification is essential for accurate results.

Do All Lab-Grown Diamonds Test the Same?

Not every lab-grown diamond gives the same test results. CVD stones and HPHT ones often react in different ways on electrical testers. You need modern machines to tell their growth styles apart with confidence.

Should a Lab-Grown Diamond Be Removed From Its Setting for Testing?

Taking a lab-grown diamond out of its setting can help you get much clearer results. The metal around the stone may block testers and mess up thermal or electrical readings. This step makes sure the test measures the diamond itself.

How to Tell if Diamonds Are Real Without a Tester?

Try a few simple checks. You can breathe on the stone and watch for fog. Look closely under a magnifier to spot tiny flaws. Drop it in water to see if it sinks fast. A real diamond will clear quickly, show natural marks, and fall right to the bottom.

Conclusion - Don't Let the Tester Fool You

Never rely solely on a quick diamond tester before making a purchase. Some of the best tools still give confusing results, especially when checking CVD lab diamonds. It is helpful to obtain a grading certificate issued by a trusted laboratory, such as GIA or IGI. This proves both the diamond’s authenticity and its quality.

You might also want to let a skilled gemologist inspect the stone. A trained eye can see growth marks that small gadgets simply can’t pick up. Taking this extra step keeps your money safe. It also gives you complete confidence that your diamond is genuine and worth what you paid.

Need help in choosing your authentic lab diamond jewelry? Call (213) 306-7211 or book an appointment with our experts.