How to Tell a Fake Diamond from a Real Diamond – 8 Different Ways

Real diamonds vs Fake diamonds

Have you ever wondered how to tell a real diamond? How do you know if a diamond is real or fake?

How to spot a real diamond from a fake diamond

Different kinds of fake diamond

A real and fake diamond look very similar. There are simulant and synthetic diamonds.

Many ‘fake’ diamonds look alike. In our post today we’re going to show you some ingenious ways how to tell a real diamond from a fake.

By using just one of our tests, you will learn how to tell if your diamond is real. Or is your diamond a worthless imitation? Some of the following criteria need the stone unset from the ring mount.

What are Synthetic Diamonds?

A synthetic diamond is also known as a lab-grown diamond. Other names include a cultured diamond or a cultivated diamond. They are produced artificially, unlike natural diamonds formed in the Earth.

Please note that our tests will not identify lab-created diamonds. Most lab-grown or created diamonds include a tiny inscription identifying them as lab-grown for this reason. You might see small writing on the girdle of a real diamond or a lab-created stone.

What are Diamond Simulants?

Diamond simulants fall into the category of imitation diamonds—stones with gemmological features similar to the real thing. Diamond Simulants differ from synthetic diamonds. In contrast, Synthetic Diamonds are actual diamonds having the same material properties as natural diamonds. For this reason, most of our tests help to identify a diamond simulant from a real one. 

The following make perfect tests at home for testing fake diamonds. Some tests suit loose diamonds, while others suit diamonds already set.

1. The Line Test

How to tell a real diamond from a lookalike diamond - the line test

The line test involves placing the stone on a single black line drawn on paper. It’s a great way how to tell a real diamond from a fake. The line test appears much more visible through a fake diamond. Place a diamond over the black line and watch the line disappear. White light bends when passing through a diamond. 

2. Check the weight and size of your diamond

A diamond of any given size will achieve a reasonably typical carat weight. For example, a 5mm round diamond will weigh close to 0.50cts (give or take a few points.) A CZ of the same size tends to way far more substantial, and this is a straightforward sign that the stone is not a diamond. You can check the size and weight of your diamond against our online size chart.


round diamond sizes compared

3. The breath or fog test

Some diamond experts use a breath test to spot a real diamond from a fake. When you breathe slowly on the surface of a diamond, moisture beads finely over the stone, disappearing very rapidly. The reason is the thermal conductivity. The fog disappears gradually from a non-diamond. For this reason, diamonds serve a use in electronics. Lab-grown wafer-thin examples make an ideal thermal conductor for circuitry. Diamonds are the best thermal conductor on Earth.

4. Touching a rock with your tongue

Not strictly tasting the stone, but some seasoned experts can tell a real diamond by putting it against their tongue. The icy feel of the diamond on account of the thermal properties is very subtle and difficult to detect. A diamond will take heat away from the surface of your tongue. Diamonds are very good at dispersing heat. For this reason, lab-grown diamond wafers make great thermal conductors for electronic circuits.

5. Does your diamond look too perfect?

Here, we must be careful, since white, flawless diamonds do exist. Many synthetic/simulant diamonds imitate entirely white bright diamonds free of any inclusions. If the stone appears very white and free of any small marks, you could have a fake. Or, you might be holding a costly diamond! CZ’s often appear almost purple-white compared to diamonds. For this test, you need a 10X loupe or a magnifying glass. We grade diamond colour using a scale starting at D colour. Some imitation diamonds appear too white. However, some gemstones set into Yellow Gold pick up colour from the metal colour, appearing less white. For this reason, most gems are colour graded loose.

6. How sharp are the facets on your diamond?

Compared to diamonds, many replica stones, such as Cubic Zirconia have more rounded edges to each facet. Diamonds appear sharper and keep this sharpness. Compare a diamond to a CZ under a 10X jewellers lens, and upon looking closely, this will be noticeable.

Lila engagement ring with heart shaped underbezel

The Lila engagement ring in white gold set with a large simulant for display purposes. (From the SD showroom.)

7. Is there wear on your diamond?

Diamonds rarely wear. Diamonds can sometimes appear ‘smoked’ when a stone burns under high temperature—a skin results on the stone which requires polishing to remove. As a result, a smoked diamond reflects light in a reduced way with a dull surface.

Diamonds tend to keep their sharp, perfect polished facets for life. For this reason, they outperform other gems for engagement rings. Cubic Zirconia and other replica stones wear more quickly. Non-diamonds wear on the joins between facets. This detail appears under a jeweller’s lens or magnifying glass. Do not confuse wear with chips, polish marks or natural inclusions on the surface of the diamond.

Most people know that it takes a diamond to scratch another diamond. In fact, diamonds rarely pick up scratches unless it is from another stone of the same type. On Mohs scale of hardness, diamonds are 10 on top of the list.

Rough materials such as sand-paper scratch diamond lookalikes, but not a real diamond. We do not advise this test to be carried out on any item unless there is no fear of damage. Most precious metals scratch easily, so be careful when considering this test.

8. Does your diamond have small marks?

Most natural diamonds have marks within the diamond. We refer to these as inclusions. If you can see small marks within your diamond, the chances are that your diamond is real and not a fake. Diamonds are graded under 10x magnification to grade their clarity. Many items of cheaper jewellery feature diamonds with more substantial inclusions. Some might call these natural diamonds or diamonds of a commercial grade.

GIA and IGI clarity grades compared

Ask an expert if you can’t tell a real diamond from a fake diamond

If you’re passing our showroom in Ryde, feel welcome to drop. We’ll be glad to test your ‘fake diamond’ to see if it is real. We test third-party ‘diamonds’ often. If your gemstone is genuine, or not, we can set your stone into one of our designs. We must, however, identify your stone before any work starts. Please just get in touch for a quote to set your stone into one of our many settings.

Why does a diamond glow under UV light?

When a diamond glows under UV light, this does not mean you have an artificial or fake diamond. Some diamonds reflect UV light in varying degrees. As a result, some diamonds appear to glow under intense UV light. Read more on Fluorescence in our education section of the website.

Gemstone diamond lookalikes

For reasons of cost, some buyers search for lookalike diamond gemstones. Many transparent white gems stand in for diamonds. Some cost far less than diamonds. But many lack the hardness and dazzle of a diamond. Here are just some gemstones used as diamond substitutes.

White Topaz

White Topaz costs far less than other gemstones. Also, White Topaz occurs in various fancy shapes. Some buyers use White Topaz instead of a diamond. Real diamond shoulders work well alongside Topaz. These add an element of ‘real diamond’ to a ring.

White Topaz one of the gem stones that look like diamonds

White Topaz gemstone looking very similar to a diamond. 

White Sapphire

Perhaps the best fake diamond substitute. Despite White Sapphires lacking the same ‘fire’ like a diamond, they are durable. Both Sapphires and diamond make tough gemstones, well suited to rings worn every day.


Moissanite was discovered in 1893 by the Nobel Prize-winning chemist Henri Moissan. He found the natural form of this gemstone within a meteorite in Arizona. At first, mistaken for diamonds, he later established the crystals were formed from Silicon Carbide. Owing to the rarity of natural Moissanite, almost all Moissanite is lab-grown. Furthermore, this diamond alternative appears similar to diamond, with visual differences. For example, the brilliance of both types of gemstone differ.

Lab-grown diamonds

Lab-grown diamonds look identical to real diamonds, with the same physical appearance and properties. For this reason, most feature an inscription on the girdle of the stone. The words “lab-grown” appear to avoid any confusion with the genuine article. 

lab-grown diamonds include a laser inscription on the girdle to identify them as lab created diamonds

Lab-grown diamonds work out less expensive than natural. We provide lab-grown alternatives to our rings upon request. Please contact us for a quote on our lab-grown options to any of our engagement rings. 

Mark Johnson

About Mark Johnson

Mark attended Liverpool University and went on to pursue a career in the diamond industry. After more than a decade working in polished diamonds, Mark moved to the Isle of Wight where he launched Serendipity Diamonds. He works most days from their busy Ryde showroom, photographing jewellery and writing for the Serendipity Diamonds website.

Mark Johnson

About Mark Johnson

Mark attended Liverpool University and went on to pursue a career in the diamond industry. After more than a decade working in polished diamonds, Mark moved to the Isle of Wight where he launched Serendipity Diamonds. He works most days from their busy Ryde showroom, photographing jewellery and writing for the Serendipity Diamonds website.