How To Tell If a Diamond is Real With a Flashlight Plus Other Simple Tests 

 October 31, 2021

By  Clark Pawners & Jewelers

 woman wearing a diamond ring

There are many diamond tests suggested but do you know one of them is how to test if a diamond is real with a flashlight?

A diamond is one of the most expensive gemstones globally, and according to Forbes, a red diamond is the number one most costly stone with a whopping $1,000,000 value per carat! No wonder the most coveted engagement rings are made from it.

For a typical buyer, every gemstone that looks like a diamond seems the real thing.  But how do we know how to tell if a diamond is fake?  There are ways to test a diamond that can be done wherever you are. 

Are These Tests Effective in Telling if a Diamond Is Real?

There are so many written DIY home tests that claim to help tell if a diamond is real or not.  Let’s see how these tests are done and if they deliver as promised.

The Flashlight Test

They say a flashlight is also an excellent tool in detecting fake diamonds. This is done by holding the flashlight vertically, pointing the light upwards, and positioning the stone upside down on the lens.

Observe how the light from the flashlight goes through and through the stone.  What do you see?  Do you see rainbow colors on the surface where the beam from the flashlight exits the stone?  Or do you only see a white light?  

Fake diamonds do not reflect spectral rays from the beam of the flashlight.   This is because a diamond’s refractive index is high; it makes the white light entering the diamond split into multiple colors before it exits on the other side of the stone. 

Again, if it does not reflect colored light, the stone is not genuine.

How reliable is this?

This test is not reliable as effects vary.  Even professionals have a hard time relying on this test as it does not deliver its promised results.

The Fog Test

A quick way to tell if a diamond is real or fake is through the Fog Test.  Before doing the procedure, the first thing to do is make sure the diamond is clean and not greasy. 

Then, put the stone in front of your mouth and breathe on it until it is covered with fog. If it clears up after one or two seconds, be happy you’ve got the real diamond!  But if the fog stays for more than two seconds, then it must be a fake.

A real diamond can disperse heat immediately because it has excellent thermal conductivity and heat dispersion properties; that’s why it is impossible to fog up.  If you compare a diamond to stimulants like Moissanite, you may be confused as they may have similar dissipation times.

Is this effective?

The fog test works for diamonds that are unmounted or unset.  You may get a Cubic Zirconia that’s also loose and the diamond that you want to test and place them both on a piece of paper and breathe on them.  If the fog on the diamond is gone simultaneously as the fog on the CZ, then your supposedly diamond is nothing but a fake.

What is a Cubic Zirconia (CZ)

A Cubic Zirconia (CZ) and a real diamond may look similar at a glance, but though it does, it still does not compare to the hardness of a diamond.  Also, a Cubic Zirconia shines less than a diamond because of its lower refractive index.

In fact, Cubic Zirconia (CZ) is the cubic crystalline form of Zirconium Dioxide (ZrO2). Cubic Zirconia is a synthetic, colorless gemstone. 

Although Cubic Zirconia appears extremely rare within the mineral baddeleyite, they are created exclusively inside laboratories and are commonly referred to as synthetic diamonds.

The Water Test

Another easy way to know if your diamond is real or fake is by doing this procedure. Take note, though, that it’s not 100% accurate.  

Get a glass and fill it with water.  Then, drop your gemstone in the glass. If the diamond is real, it will sink to the bottom and float when it’s fake.  

Remember that not all fake diamonds float in water, so you must try the other tests to be more sure.  Weaker gems such as CZ crack because of its quick expansion and contraction caused by the heat.

Does this help?

This doesn’t help much in testing if your diamond is real because many imitations sink, just like a real diamond.

The Black Light Test

You will use a black light test to tell if your diamond is real or fake.  Turn off your lights at home and use your black light instead.  Once your black light is turned on, hold the stone under the UV light.  

Most diamonds will have a blue-colored glow, but if you see the slight green or yellow fluorescence instead, you’ll need to seek the opinion of a professional jeweler as this may mean your stone is not genuine.  

Although this is not 100% sure, it would be best to have it checked by a reputable jeweler.

Is this effective?

You’ve read that most diamonds emit a blue-colored glow when placed under a UV light.  But some don’t, and this doesn’t mean that the diamond is fake.  Simply put, some diamonds do not glow under UV light. So don’t panic yet.

The Loupe Test

Jewelers use a loupe to inspect diamonds for their class and clarity to see minute details in examining jewelry.  You may purchase a loupe on Amazon, and they’re sold at reasonable prices.  But if you want an expert instead to look at the diamond, he surely has a loupe to use.

Using the loupe, you may look for blemishes and imperfections in your diamond.  A real diamond has natural features that can’t be faked – such as inclusions.

Is the Loupe Test the answer?

Experts use the loupe, and a high-caliber loupe is needed to see minute details like the VVS to VS1  inclusions.  But using a loupe with a low magnification and poor quality will only give false or unreliable inspection results.

The Scratch Test

This test effectively determines the hardness of a gem and is a simple way to tell if a diamond is natural.  It is done by scraping the loose gemstone onto a mirror to see If the gem could scratch the stone or the mirror. 

You know that a diamond is the hardest natural substance, right?  But there are also fake diamonds like cubic zirconia,  moissanite, and many others that are scratch-resistant and very durable.

Is it effective?

Cubic Zirconia, White Sapphire, and moissanite, for example, go in the way of this test for being scratch-resistant.  So, it is not very effective.

The Magnifying Glass Test

Perform this test by looking through your diamond using a magnifying glass.  Hold it up, and look for imperfections within the gemstone. 

Most diamonds have imperfections called inclusions. A natural diamond could also be flawless, and those lab-created diamonds or what we call synthetic diamonds.

How effective is this?

Looks can be deceiving, and some diamonds can be internally flawless, although this is very rare, and many have inclusions.  So, this makes the magnifying glass test not too reliable.

Diamond ring on a wooden table

The Sparkle Test

The sparkle test will make you understand the optical properties of a diamond more.  Simply hold the loose diamond near a light source, like a lamp, and see the reflection of the light from the diamond.  

This test will be best if there is another gem that you’ll compare along with it, like cubic zirconia.  You’ll see how different their effects are to light.

Is this procedure reliable?

No. This sparkle test is not very reliable because an untrained eye may find it hard to recognize the difference between a real diamond and a fake by observing how it sparkles.  

We all know that some diamonds with heavy inclusions and low grading will not sparkle that much.  And there are lab-created diamonds that can deliver the spark expected from natural mined diamonds.

The Newspaper Test

You’ll need a newspaper and be in a well-lit area to make sure there will be no shadows casting over the stone or the newspaper. This procedure highlights how diamonds bend, bounce, and refract light. 

The goal is to see if you’ll not be able to read through the stone placed over the print on the newspaper.  If you can read the letters the stone is fake. 

A real diamond will refract the light in several directions from its many facets that will hinder you to see clearly through the diamond to read the prints on the newspaper.

Is it able to tell a real from a fake?

This newspaper test only works for loose stone, well-cut rounded natural diamonds.

The Dot Test

You will need a piece of white paper and a pen to perform this test, and make sure the area where you’re doing the procedure is well lit.  Draw a small dot on the paper and place the stone with the flat side touching the dot. 

Now, make sure you are viewing through the pointed part of the diamond, looking down at the paper.  Then, look closely inside the gemstone. Once you see the dot reflected inside it, the diamond is a fake. But if you don’t see the dot through the stone, it is real.

Is this a good test?

This dot test will not work with moissanite either and will only work with loose diamonds for well-cut round diamonds that are unset.

The Heat Test

You’ll be needing a cold glass of water and a pair of fire-resistant gloves for this procedure.  Heat the stone for 30-40 seconds, then immediately submerge it in the cold water.  This may seem scary because only two things may happen; it will not react in any way or shatter to pieces.

How effective is this?

Among the home tests, this procedure is the most hazardous and not safe to be performed.  Real diamonds are heat resistant because they can disperse heat or not let heat affect them.  This ability to disperse heat is why this precious gemstone is also used in microelectronics and other industrial tools.

The Mount Test

Checking the number of diamonds in a ring is also an excellent way to tell if a diamond is real.  A real diamond is only set in high-quality jewelry such as platinum, yellow gold, white gold, pave or side-stone, and the halo setting rings.

Look inside the ring for the markings to make sure the setting is genuinely what it claims it is. The markings 10K, 14K, and 18k are for the types of gold used.  PT and karat mean platinum. 

When you see 585, 770, 900, and 950, these tell you that platinum or gold was used.  A “C.Z” means cubic zirconia and not a real diamond.  And also, if you see a .925 or the Argentum Silver marker, it could be a fake diamond.

Does this work?

This test is not easy for ordinary people who do not know much about mountings and diamonds. This test is not easy and does not assure a reliable result, especially if the cracks are hidden behind the mountings.

The Diamond Tester Test

Have you seen a diamond tester?  It is so handy that you could just put it in your pocket.  It has a needle-like tip that needs to touch the stone that you’re testing.  It will flash the indication on its display, telling you the diamond is natural, or you’ll hear a sound signal.

Because diamonds are superconductors of heat, the diamond tester could also be fitted with a copper heat probe to analyze the thermal conductivity probe of the stone.  

The thermal conductivity test is one of the most accurate diamond tests, except for its limitations compared with moissanite, which has the same thermal conductivity.

Is this effective?

Jewelers use diamond testers to tell if a diamond is genuine or not.  It has been proven that diamond testers are one of the most accurate tools.  

The only problem is that a thermal conductivity test can confuse moissanite for a diamond because both of them conduct heat.  So, to solve this issue, an electrical conductivity test is best to use in testing stones because moissanite and diamonds conduct electricity differently.

A miner cleans off a mined diamond.


What are the Other Uses of Diamonds?

As the hardest known substance, a diamond has found its vast role in the industrial world.  Having the highest thermal conductivity plus being chemically resistant makes a diamond valuable where durability is needed.

A real diamond has a high index of refraction, adamantine luster, and high dispersion.  These properties make a diamond the world’s most sought-after gemstone.

Beautiful diamonds in macro.


We are so familiar with the fact that diamonds are used as jewelry.  It is famous and expensive.  This is probably the reason why the coveted engagement ring has it.

Truing Grinding Wheels

Truing or dressing is a sharpening process that returns a wheel to its original shape and performance.  Using a diamond in its machine cleans away clogged areas between the diamond grains and, at the same time, restores the profile and shape of the wheel’s edge.

Wire-drawing dies

Wire drawing is the process of making a smaller wire diameter using a tool with a conical hole. The hole of the tool has a different diameter on each side because its entrance is vast and its exit is small.  Diamond dies have superior durability and are more precise.

Cutting Tools

Do you believe that diamond is not only famous as a stone but also a widely used cutting tool?

Being the hardest known substance made it attractive as an industrial cutting tool.

Manufacturing Cars

Nissan has revealed the details of its manufacturing process, which employ diamonds to make engines more efficient.


Diamond windows are used to cover openings in lasers, vacuum chambers, and x-ray machines.  They are transparent, heat and scratch resistant, very durable, and made from thin diamond membranes.

Heat Sinks

Materials that absorb or transmit excess heat are called heat sinks.  Since diamond has the highest thermal conductivity, it is perfect for conducting heat away from heat-sensitive parts of high-performing microelectronics.

Real diamonds  with black background.

How can you tell real diamonds from your eyes?

With people, looks may deceive us.  This also applies to diamonds.  But how can we tell if it is a real diamond we have just by looking at it?

We can tell a diamond is real when it reflects in shades of gray.  

Does a real diamond sparkle rainbow?

When your diamond sparkles a rainbow of colored light, then most likely it is a fake diamond.  Again, when it is a natural diamond, you will see shades of gray in its reflection.

How do you test a diamond with a lighter?

Some also do the lighter test to tell the difference between a natural diamond and a fake diamond.

Light the stone using a lighter for about 30 to 40 seconds, then drop it in cold water.  If it shatters to pieces, then it’s a fake diamond.  The natural diamond won’t react to it.

How much does a natural diamond cost?

An average GIA-certified natural diamond ranges from $8,000 to $84,000 depending on the cut, carat, clarity, and color.  A fake diamond will obviously cost less.

To Sum it Up

A natural diamond, though worth a fortune, is also worth it.  If you can afford to purchase a real diamond, don’t hesitate to own or buy one for someone special to you.  It is also an excellent way to preserve memories.  It is a significant investment or family heirloom.

It is advisable to learn more about diamonds before purchasing one because you will be able to contribute to their value. Not to mention it is the hardest substance known to man.

Being the hardest substance means being wanted by most industries.  Besides being a woman’s best friend, diamonds are also used in cutting tools, manufacturing cars, truing grinding wheels, wire drawing dies, x-ray lenses, and many more.

It is a great skill if you know how to tell if a diamond is real or fake. These tests may be done at home: fog test, water test, scratch test, blacklight test, mount test, loupe test, magnifying glass test, scratch test, flashlight test, etc.

But take note that, as always, it is much better to consult a local diamond expert and have the confidence that your diamond is genuine and not a fake.


If you want to purchase one and need expert advice, contact us.  At Clark Pawners and Jewelers, you will always be confident in your diamond jewelry purchases.

Clark Pawners & Jewelers is your trusted pawn shop in Chicago. We buy and sell jewelry, diamonds, gold and more, aside from offering cash loans.

Clark Pawners & Jewelers

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