How to tell if a diamond is real

By 13.03 September 20th, 2018 No Comments




Knowing how to test if a diamond is real or fake is important when purchasing diamonds.
If your purchase comes with a genuine GIA, IGI or AGS certificate and the stone matches the certificate, then be assured that this stone is real. However, it is possible that some jewellers and gemologists may be fraudulent dealers, so it is to a buyer’s advantage to know how to test diamonds, whether the stone is a loose or a mounted stone. Before signing on the dotted line, ensure the stone’s authenticity.

If you are purchasing diamonds online, it is of paramount importance to obtain a certificate as certification and grading will assure you that the stone has been proven real by the experts. The certificate must come from a grading authority such as GIA or AGS or an independent appraiser who is affiliated to a professional organisation such as the American Society of Appraisers.

Fake diamonds are made from stones like cubic zirconia and moissanite, white topaz and white sapphires, and can often be mistaken for real diamonds. Take precautions and become educated in knowing if a diamond is real or not by noting the pointers below.

For diamonds that have been inherited that you want verified, then home tests will help, along with tests done by a diamond expert using specialised equipment.


Testing Methods for Real vs Fake Diamonds

There are a few very basic tests for testing fake vs real diamonds such as the fog test, checking the setting, a scratch test and seeing through a real diamond test.

The Fog or Breath Test is the most simple of all the known tests.

Diamonds are efficient conductors of heat, so hold the stone or ring in front of your mouth and ‘fog’ it as you would fog a mirror by breathing on it with a puff of air. The fog will form on the stone due to the moisture and heat in your breath. The fog should disappear immediately on a real diamond, whereas on a fake stone the fog will remain for a few seconds. If you have real and fake stones, then check these together and witness the condensation that will build up on the fake stone.


Can you see through a real diamond?

You should not be able to see through a mounted diamond – if you can it is likely that the stone is a fake and may be glass, quartz or cubic zirconia, which are able to mimic a diamond’s brilliance but which have lower refractive indexes.


Do real diamonds sparkle in the dark?

Diamonds get their brilliance from reflection, refraction and dispersion. Reflection is the light that hits the diamond and is bounced back up, giving it an instant shine, so diamonds never shine in the dark.


Scratching Glass

Diamonds are hard enough to cut glass but some synthetic gemstones can also do this, so this is not a definitive test for real diamonds, as was once believed before the advent of hard synthetic stones.


Check the Setting and Mounting of the Stone

A real diamond will, in all probability, be set in an expensive gold or platinum setting, not a setting made of cheap metal. The setting can be checked by looking inside the centre of the ring for a metal marking such as 10K, 14K or 18K for gold settings or PT or Plat for platinum. Certain numbers such as 585, 770, 900 and 950 also indicate theses metals. Cubic zirconia settings should be engraved with a CZ stamp.


A jeweller’s loupe is a special magnifying glass used in the jewellery industry.

12x-21-mm-jewelers-loupeA loupe does not have a handle and its lens frame is conical. Looking at a stone through a loupe, a real diamond will manifest various imperfections such as external blemishes and/or internal inclusions such as small flecks of minerals or slight colour changes, whereas a fake diamond may most likely appear as being perfect. However, a real diamond can be flawless, although these are rare. Use other factors as well to determine whether a diamond is real or not. Bear in mind that laboratory-created diamonds, produced in controlled environments, generally do not have any imperfections: they are ‘real’ but they are not ‘natural’.



Using a Microscope

A jeweller using a 1200x magnification on a power microscope will be able to see inclusions found in real diamonds. If a slight orange flash along the facets is seen, the stone may be a cubic zirconia.


The Water Test

Fill a normal drinking glass ¾ full with water and carefully drop a loose stone into the glass.
A fake stone will float at the top of the surface or in the middle of the glass, whereas a real stone will sink as diamonds have a high density.


Heating the Stone

Heat a stone with a match or lighter for about 40 seconds using plyers and a fireproof glove. Drop the stone directly into a glass of cold water. A real diamond will remain as is but a fake stone will shatter. Weak materials such as glass or cubic zirconia will crack and shatter due to the rapid expansion and contraction of heat. Diamonds are composed of very strong materials which are unresponsive to heat.


Heat Probe Test

This professional test measures how long the diamond retains temperature. It takes about 30 seconds and is often done at no charge.


Combination diamond/moissanite testing

The heat probe test does not distinguish between diamonds and moissanite – in this case an electrical conductivity test, not a thermal test, needs to be done.


The Ultra-Violet Light Test

When placed under ultra-violet light most diamonds emit a blue-coloured glow, but this test is not definitive as some diamonds do not react to UV light. Also some fake diamonds are ‘doped’ so that they glow under UV light.


X-ray Examination

These tests can tell if a stone has a radiolucent molecular structure (does not appear on an
x-ray image) or a radiopaque molecular structure (shows up clearly on an x-ray). Fake stones have more radiopaque features than radiolucent features.



Diamonds refract or bend the light passing through them resulting in the brilliant appearance, an inherent property of the stone. Fake diamonds sparkle much less, if at all.

The Newspaper Method:  Place the stone upside down on a piece of newspaper. If you are able to read the print, or see black smudges, it is likely that the stone is a fake.

The Dot Test:  Draw a small dot with a pen on a piece of white paper and place the stone over the centre of the dot. Look directly down on it. If the stone is not a diamond, you will see a circular reflection in the stone. You cannot see the dot through a real diamond.



If you see rainbow reflections, the colour of the refracted light, when looking down through the top of the diamond, then the stone is either a low quality stone or a fake. A real diamond’s reflection appears as shades of grey. Rather check for ‘sparkles’ which are associated with a stone’s brilliance or intensity of light refracted by the cut of the stone.

Hold the diamond under a normal lamp and watch how light reflects off the stone. A real diamond reflects white light very well resulting in ‘sparkle’. They also reflect coloured light, known as ‘fire’.

Moissanite can be confusing and may show rainbow colours, resulting from double refraction – this is not a property of diamonds.


High Sensitivity Weighing

Cubic zirconia weighs approximately 55% more than diamonds with the same size and shape.
A high sensitivity scale which measures down to carats and grains is necessary for this comparison.


Many of the above tests will help in determining if a diamond is real; however, it is to your best advantage to have any diamond tested by a professional diamond expert as they know how to spot a fake.


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