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How Does a Diamond Tester Work on Lab Diamonds?

How can you tell if a diamond is real or not? Despite word on the street, the average human truly can’t tell the difference between a real diamond and a high quality simulant (aka a fake) just by looking at it. On the other hand, any well-trained gemologist can just pop that sparkly rock under a microscope and determine pretty quickly if what you have is worth it or worth nothing. So how are us everyday folk supposed to know? One of the most surefire ways: A diamond tester! Yes, there is a cool little gizmo that uses thermal or electrical connectivity to help you determine if your diamond is legit. One speed bump? Lab diamonds. Here’s the scoop:

custom frank darling engagement rings on a hand
Lab diamonds come in all shapes and sizes, so there is no shortage of options when choosing your perfect lab diamond!

Nerd Alert

You’ve heard all about it: the beginning is a very good place to start. So how does a diamond tester work…at all? Well, there are two basic kinds. The first works via thermal connectivity and will help separate real diamonds from everything else, with the exception of Moissanite. The second works via electrical connectivity and will separate real diamonds from everything else including Moissanite. What’s with Moissanite? Well, it transfers heat too similarly to diamonds, but conducts electricity differently, hence the second type of tester to rule that one out.


Both types of diamond tester are small, portable, pen-like instruments. By placing the needle-like tip on the surface of the rock in question, the tester will detect the heat or electrical transference of the stone and alert you with a little light or sound display as to the authenticity of your stone. Ta-da! But now you’re probably wondering: Are diamond testers actually reliable? Short answer: yes. They’re one of the most accurate ways to tell the difference between a real diamond and, well, something else.

A diamond tester will test the hardness and chemical components of your diamond!
Diamond tester closeup inclusion
Flux can be reflective since it’s metallic. Credit: GCAL
Diamond tester closeup inclusion
Flux under extremely high magnification. Credit: GCAL
Can you tell which one of these emeralds is lab?

Not Something Else

Now here’s the burning question: If you use a diamond tester on a lab created diamond, will it pass? Long answer ahead. But first, another type of test:

We didn’t think so. And here’s why: Lab created diamonds are real diamonds, period. They are sparkly, envy-inducing, conversation-starting chunks of carbon that we, as humans, can’t seem to get enough of. In fact, in 2018 the FTC ruled, “The Commission no longer defines a ‘diamond‘ by using the term ‘natural’ because it is no longer accurate to define diamonds as ‘natural’ when it is now possible to create products that have essentially the same optical, physical, and chemical properties as mined diamonds.”

This lab grown 2 carat CVD
marquise diamond has a dreamy symmetrical look.

Pass or Fail

Because lab grown diamonds do have all the same properties of natural, mined diamonds, they will test as real on a diamond tester. I mean, after all…they are real. And a diamond tester is meant to help you sniff out fakes. So what is a fake, then? We thought you’d never ask.

Besides plastic, glass, silly putty…a diamond tester will help you sort out all the most common diamond simulants. What’s a simulant? Any material (other than diamond, obvi) that is meant to simulate the look and sparkle of a diamond. This includes things like cubic zirconia, Moissanite, white sapphire, quartz…and plenty of other hybrid materials with fancy acronym names trying to pull one over on the unsuspecting public. All these materials will conduct heat and electricity at different rates, alerting a diamond tester that they aren’t the real deal. Are they all bad? No. They’re just not diamonds.

A flat cloud of black inclusions seen in a CVD diamond. Credit: GCAL
A single sharp plane that appears in CVD diamonds. Credit: GCAL

One of These Things is Not Like the Other

Back to lab created diamonds. If they’re not simulants (they’re not), and you can’t use a diamond tester to determine their true identities (you can’t), then how exactly are you supposed to tell the difference? Well, spoiler alert: a trusted gemologist can help. We could tell you all about different diamond types or the inclusions specific to lab created diamonds…but these are not things you should try to make judgements on without the proper instruments (photoluminescence spectroscopy, amirite?) and training. That’s why diamond grading labs exist! What you can make judgements on, however, is what diamond is right for you. Or not a diamond, that’s cool too.

Custom Frank Darling lab diamond tester stack.
Can you believe this custom stack is all lab diamonds?
Can you tell which of these three elongated cushion cut diamonds is lab grown and which is natural?

Have a Penny, Save a Penny

One of the biggest reasons to go lab grown? Price. If you’re working with a tight budget but want a high quality diamond, a lab grown can get you what you want for 40-50% less than the cost of a comparable mined diamond. How is this possible? Well, the diamond industry hasn’t always been so keen on lab grown diamonds (probably not surprising when the upstart techy dude wants to replicate the product you’ve built your brand on). It’s only within the last handful of years that lab created diamonds have started to really make a name for themselves—thus becoming more widely available in a wider range of qualities. 

Climate Control

We probably don’t need to tell you, but the environment is kind of a thing these days. And diamond mining is pretty unsustainable. But both lab created and mined diamonds have an impact on the Earth as we know it. The industry likes to give you the headlines, but you deserve to know more. Like, that mined diamonds use 500 million joules of energy per carat, whereas lab diamonds use about half that. Some growers are even going so far as to use entirely renewable energy. Not to mention the major differences in water usage, land use (hello, one you don’t even have to dig for), and the overall carbon footprint. Ok, we’re mentioning it. Mined diamonds produce more than 125 pounds of carbon per carat. Lab created diamonds produce just less than 10. 

Report Card

One other little detail to know? Despite the growing popularity of lab created diamonds, the GIA still does not provide a full standard grading report for them. Because of this, the price and value of a GIA-graded lab diamond will be affected. There are other labs, however, who are stepping up to the plate. IGI and GCAL both offer full grading reports for lab grown diamonds, and all of Frank Darling’s lab diamonds will come with one of these labs’ certificates of authenticity.

Custom Frank Darling engagement rings in various styles.
Different grading institutions have their biases, which is why it’s way more important that you like your stone in person!

Your Ring, Your Way

Still need some help deciding what’s right for you? Book an appointment at our New York salon to view certified lab-grown and natural diamonds in person. Or check out our diamond search where you can view 360-degree images of more than 10,000 diamonds and don’t forget to zoom out (because size can be deceiving). Not finding your dream diamond? Email us with what you’re looking for at We’ll curate a list of 5-7 exclusive stones that are just right for you.

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