Testing for synthetic diamonds

ARI                               ARETE

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We are unique in giving a very detailed appraisal of every product, telling you it’s features and its limitations. Every tester has its limitations, no matter what the make, no matter who you buy it from. This is a specialist article about synthetic -diamond testers. If you are are new to the subject you will find our guide to buying diamond testers and guide to buying electronic gem testers more useful to start with. You might also be interested in specifically in testing for Moissanite


Synthetic-diamond testers are for professional jewellers and diamond dealers who know that they have a diamond and want to know the chances of it being a synthetic diamond or a natural diamond. But you MUST be certain that you are testing a diamond.  

"Natural" means dug from the ground (mined). "Synthetic" is identical but grown in a laboratory (lab-grown, lab-created, manmade). You cannot use a standard diamond tester - that will only tell you if the stone is diamond or not diamond, and both synthetic and natural diamonds are diamonds.   

A synthetic-diamond tester helps screen out Type II diamonds. Currently, all synthetic (CVD and HPHT) diamonds are Type II. However, 2% of natural diamonds are also Type II. So when you get a reading, "CVD / HPHT / Type IIa Diamond" it means there's a 98% chance of it being synthetic. 

As an extra feature, these testers also test for Moissanite. This means you can use a relatively inexpensive diamond tester alongside a synthetic-diamond tester to get the most reliable results of all (e.g. Diamond Experior, half price if you tick the 'optional extra' box when buying the Arete).

These testers only work on stones that are:

  • brilliant-cut. They usually give false readings on shallow-cut including all simple / rose-cut. They often give false readings on fancy cuts. 
  • size 0.02 to 10 carat.
  • colour D to J. 

If you don't understand the above, these testers are not for you, they are for professional jewellers and diamond dealers. Please see our standard diamond testers priced at £12.50 to £350.00  and/or see our guide to Buying Diamond Testers). 


Natural diamonds originate as crystals that grow, naturally, deep in the earth, they take 2 to 3 billion years to grow. We tend to just call these diamonds without feeling the need to say that they were mined.  

Synthetic diamonds are grown by man in a laboratory (using the same formula nature uses), they take a few weeks to grow. "Synthetic" is the scientific term. Colloquially, these are advertised as lab-grown or lab-created  or manmade diamonds.

Before you use a synthetic-diamond tester you must be certain you are testing a diamond. If you don't know if you have a diamond, then you need a standard diamond tester. Please ignore the remainder of this article and see our Guide to Buying Diamond Testers.

Natural diamonds and synthetic diamonds are the same:

  • They are the same chemically (carbon)
  • They are the same physically (same crystal structure, hardness, density)
  • They are the same optically (refractive index, reflectivity, dispersion)
  • They can appear the same visually (when examined with a loupe). 

However, most synthetic diamonds react differently if you shine an ultra violet laser through them and measure the response (UV fluorescence), so you can tell the difference (mostly) but it's difficult to do, which is why these testers are so expensive. 


Synthetic diamonds of any significant size (over 1/2 carat) are usually laser-engraved around the edge (girdle) with a serial number. The engraving is a fraction of a millimetre tall, to see it you will need a special extra-powerful magnifier or, better, simple microscope

Diamond experts can sometimes tell the difference by examining the stone under a good 10X loupe or, ideally, a good quality microscope to check for inclusions: black specs or tiny crystals (probably natural), fine striations or the 'seed diamond' (probably synthetic).  


Natural. Dug up out of the ground (mined)

Synthetic. Grown in a laboratory (lab-grown, manmade).

Simulant. It might look like a diamond but is not.
e.g. Cubic Zirconia / Cz (synthetic because it doesn't exist in nature)
e.g. Moissanite (synthetic, because gem-quality Moissanite doesn't exist in nature)
e.g. white sapphire (which can be natural or synthetic).  

CVD and HPHTTwo methods of growing synthetic diamonds (more about this below).

Real. Diamond is diamond. If it's diamond it's 'real' diamond. If it's not diamond it's something else. An analogy would be water.*  You would not say, "Is it real water?", you would just say, "Is it water?". 

* to make this analogy simple we'll assume the water is good enough to drink and the diamond good enough for jewellery ("gem-quality").  

Fake. This depends on the circumstances:

  • You have a ring set with a spinel, you show it to your friends, they ask if it’s diamond and you say no, it’s spinel. It’s not a ‘diamond simulant’, it’s not a ‘fake’, it’s just spinel, that’s what it is, it's a real spinel.
  • You are testing stones you think might be diamond, you are only looking for diamonds, you are not interested in anything else, ‘simulant’ means you thought it looked like (simulated) diamond but it is not diamond, it is something else.
  • You buy a ring on eBay, the stone was described as diamond, you paid for diamond, it turns out it isn't diamond, it's a fake. 


It is agreed within the jewellery industry (i.e. under the guidance of the diamond-producers such as De Beers) that jewellers should only use the description 'diamond' for natural (mined) diamonds and not  for synthetic (lab-grown, manmade) diamonds. Scientifically they are the same (see above) but politically the description "diamond" should only refer to natural diamonds.  


Our section of Gem and Diamond Testers / Electronic contains all testers. The four testers listed below are specifically synthetic-diamond testers.

The ARI tester by Presidium, £1,149.00 incl. VAT.
The Arete by GemTrue, £995.00 incl. VAT
Please visit the products for specifications.
Both of these test stones set in jewellery in addition to loose stones. 

This is how they compare:

Performance: they are just about identical, there really isn't anything to choose between them. 
Reliability / Returns / Complaints: customers complain that they get incorrect readings when testing non-diamond. I say yet again, this tester is for testing stones that you know are diamond, to see if they are natural or synthetic. It is also important to remember that there are strict conditions of size, colour and cut, especially the cut because shallow-cut stones give incorrect readings.   
Instructions: the ARETE has a large screen, instead of displaying a summary of the instructions in words, it plays videos;  the ARI does display 'prompts' on the screen but no instructions, and there is no instruction manual, you have to download it from the Presidium website. So the ARETE is better.
Ease of use: the ARETE is simpler. With the ARI you must very carefully insert the test-tip each time you use it, then diligently remove it when you've finished, which is fiddly. The test-tip is made of glass and is easily broken. With the ARETE the test-tip is fixed to the tester, more robust. So the ARETE is better. 
Size and weight: the ARI is smaller and weighs 60g, the ARETE is larger and weighs 76g. So the Ari is better.
Reputation: Presidium and GemTrue each insist that their products are better than their rival!  Both are leaders in the field of diamond and gem testing. 

Recommendation: the ARI is the best as regards size for carrying in a pocket; the ARETE is simpler to use and costs less.   

The following (cheaper) models test loose stones only, and you must test one stone at a time (you can't "screen" dozens or hundreds at a time). Our customers are mostly jewellers who want to test individual stones, and the stones will be in jewellery, not loose. For this reason, the following two models are available to special order only: 

PRESIDIUM SDS, £779.99 including VAT, special order only, not on website, delivery 3 to 5 weeks. We can send you an invoice then order one for you as soon as you pay.

This is the larger of the two models, there is room to test stones mounted in single-stone rings providing the ring isn't too large and has an open setting and can make perfect contact with the sensor.  

GEMTRUE VERITAS, £590.00 including VATspecial order only, not on website, delivery 2 to 4 months (please contact us for a more precise delivery time), we can send you an invoice and add one to our next regular order as soon as you have paid.

There are testers that screen stones in bulk, they cost £5000.00 to £10,000.00, we do not sell them. 

Q & A 

Synthetic-diamond testers help screen out Type II diamonds, these are very rare in nature (2%) but, currently, all synthetic (CVD and HPHT) diamonds are of this type. They test brilliant-cut diamonds size 0.02 to 10 carat and colour D to J.  So what does this mean? - 

 Q. What is a type II diamond?

A. Diamonds vary very slightly in their atomic structure.  This is totally irrelevant as regards quality and price, its only significance is when testing:

  • Type I happen to be natural (all of them).
  • Type II (grown by the CVD or HPHT methods)) includes all synthetic diamonds and about 2% of of natural diamonds.

So when the tester reads Natural Diamond, it's Type I, but you don't need to know that because all Type 1 diamonds are natural. When the tester reads Type II, you do need to know, it means there's a 98% chance that it's synthetic. 

Q. So does that mean if a diamond registers Type II it must be synthetic?
A. This is important so I shall repeat the answer: it means that there's about a 98% chance that the stone is synthetic, i.e. about a 2% chance that it is natural.

Q. What is the meaning of, "currently, all synthetic (CVD and HPHT) diamonds are of this type" does 'currently' imply that this is likely to change?
A. The makers of synthetic diamonds strive to make them so completely identical to natural diamonds that they cannot be distinguished, even on the most expensive machine, so one day in future there might be a synthetic diamond that is truly impossible to tell from natural diamond.

Q. What is CVD and HPHT?
A. They are two methods of growing diamonds that can be used for jewellery.
CVD (chemical vapour disposition) is a type of plating, a mixture of gases is microwaved (or treated with lasers or an electron beam) which causes diamond to crystalise around a 'base' (substrate). The main use of this method is in the electronics and optics industries to 'plate' components with diamond.
The HPHT (high pressure high temperature) method involves taking a 'seed' of diamond, and subjecting it to very high pressures and temperatures in a mixture of molten metals (just as they are formed deep in the Earth), a diamond grows around the seed.
There are other methods of synthesizing diamonds but the resulting 'stones' are too small to be used in jewellery, they are used in industrial processes.

Q. ...and the point is??
A. It is possible that, one day, someone will invent a method of growing gem quality diamonds which cannot be detected on today's synthetic-diamond testers, and that is why we say it is suitable for synthetic diamonds that are grown using the CVD or HPHT processes.

Q. These testers will test round brilliant-cut diamonds size 0.02 to 10 carat and colour D to J. What does that mean?

  • "Round" means that the tester doesn't work very well on fancy shapes
  • "Brilliant-cut" is the modern standard style, the tester doesn't always give correct results on old-cut (e.g. 'rose-cut') style, especially if the cut is 'shallow'.
  • 0.01 carat is about 2mm diameter (so you cannot test really tiny diamonds) and 10 carat is about 6mm diameter
  • Colour grade D is the whitest stone, colour grade J has a slight yellow tint, anything below J is likely to give an incorrect reading.

Q. So am I meant to be able to recognise the shape and style of cut, the size and the colour?
A. Yes, you need to be familiar with diamonds, that why we say this tester is only for experienced jewellers and professional diamond dealers. 

  • the shape is easy (e.g. you know what 'round' looks like), look up the other styles of cut on the internet
  • if you are not familiar with size, buy a diamond gauge (from £3.00)
  • you do need to be an expert to colour-grade stones

Q. I buy dozens (or hundreds) of diamonds at a time, can I pour them all into the machine to see which are synthetic?
A. No, you must test each one individually. There are many testers used for mass-testing, they cost a few thousand pounds. .

Q. Will it test other stones?
A. No, it's only for diamond. And Moissanite. 

Q. What is Moissanite?
A. It's a synthetic stone, it is not diamond, it is easily confused with diamond. 

Q. If I test a non-diamond, will it tell me it's not diamond?
A. No, these testers are for diamond only, you must be certain you are testing a diamond.

Q. What will happen if I test a stone that is not diamond?
A. It might tell you it's natural diamond, it might tell you it's synthetic diamond, it might even tell you it's Moissanite. You must be certain you are testing a diamond. 

Q. What do I need for diamond v. non-diamond (and Moissanite)? What do I  need to test other gemstones?  
A. See all electronic testers.
Read all about how to choose a diamond tester (diamond v. non-diamond + Moissanite). 
Read all about how to choose a gem tester.

Q. Is there a tester that will test all of the above?
A. No.