Guide to buying diamond testers



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ANOTHER ARTICLE

Various Diamond Selector diamond testers, which are genuine?

THIS ARTICLE IS QUITE LONG, IT IS NOT NECESSARY TO READ ALL OF IT!

CONTENTS

ARE DIAMOND TESTERS FOOL-PROOF?
BEWARE OF UNUSUAL STONES...AND ALWAYS BE AWARE OF THE OBVIOUS
DIAMOND TESTERS AND U.V. (Ultra Violet light)
MOISSANITE
DIAMOND TESTER OR MULTI TESTER?
WHICH MODEL?
CONCLUSION
TEST RESULTS

ARE DIAMOND TESTERS FOOL-PROOF?

A true story, the tale of a man who was fooled

We sold a diamond tester to a man who went to Africa to buy 'bargain' diamonds (uncut 'rough' diamonds) from a 'contact'. After a very long time haggling they agreed a price (I think it was $50,000.00), he tested the stones, they registered DIAMOND on the tester, they were sealed in a container and the he signed across the seals. The money was transferred into the seller's bank account and the following day the buyer collected the stones. The seals on the container were still intact, he brought them back to England.

Guess what? When he got them back to England he found they weren't diamonds at all. The customer rushed the diamonds over to us, we tested them on five different diamond testers - they were not diamonds.

This, in a way, was a clever 'con' - because the average jeweller will know what a cut diamond looks like, and if presented with huge stones that look 'too watery' or 'too sparkly' he will be suspicious, even before turning on the diamond tester. But very few people know what diamond crystals look like. If you are planning on parting with thousands of pounds, do some research, e.g. search Google images for rough diamond crystals to see what diamond crystals should look like.

There are other precautions you can take if you are spending large amounts of money and know nothing about diamonds.

Firstly, if the deal seems too good to be true, it's because it is too good to be true, "Cheap Diamonds" are like "cheap gold" or "cheap cash" - they simply don't exist...unless you become involved with criminal gangs. These gangs smuggle real diamonds, drugs and people, and you really do not want to find yourself in a remote part of the world, escorted by armed men to remote mines, then pressurised into parting with money.

Do not let that diamond tester out of your sight, even for a minute. They can be tampered with (by re-soldering wires inside) so that everything reads DIAMOND. Our man in Africa managed to return to England without the diamond tester, it had been "mislaid in the confusion" - what a surprise!

Keep on your person a genuine diamond (it need not be large) and a paste (glass) and a sapphire (a small synthetic sapphire will do) and test each of them before testing your purchases. You will then know if the diamond tester has been tampered with.

It is also possible, with any machine made by man, that the machine develops a fault - so use those three stones to check the machine.

Tricksters have been known to store stones in ice to cool them so that the diamond tester falsely reads DIAMOND. Try touching the stone gently against your upper lip to see if it feels icy cold, try clasping it in your warm hand and chatting to the sellers for five minutes. If they become agitated it might be because the stone is rapidly reaching room temperature and is about to register NOT DIAMOND on your tester.

These precautions do not apply to everyday dealing where the amounts of money involved are relatively small, there is no need to become paranoid. And it can happen that buying diamonds directly from the mines works out OK. I did sell a diamond tester to someone who was going to Africa but who had recommendations from friends who lived there, and he was happy about who he was dealing with and, as far as I know, the transaction was successful. Whether he made a profit I have no idea.

BEWARE OF UNUSUAL STONES...AND ALWAYS BE AWARE OF THE OBVIOUS

One stone that caused prolonged correspondence on an internet forum for gemmologists, was an unknown stone bought as 'black diamond'. It was opaque, so the usual examination of inclusions, under a microscope, was not possible; the surface was 'pitted' like granite; the SG (specific gravity) wasn't quite right; and although it certainly registered 'diamond' on a diamond tester, the results on a Moissanite tester were inconclusive, it depended on where, on the stone, the probe was placed.

Even without a gemologist spending a few hours examining and testing the stone, there were two causes for concern. Firstly, it was bought by a serviceman in Afghanistan, and most stones sold to servicemen in this area were not genuine. Secondly, 'proof' that it was natural black diamond came in the form of a lab report (certificate) from New Delhi, from "an ISO 9001:2008 Company comprising GIA alumni." A certificate is worthless unless you can check that the company (and the certificate) is genuine - and even then, you need the skill to match the stone with the certificate.

Gemmologist's conclusion: it was not diamond, it was Moissanite.

My conclusion: electronic testers are not suitable for use on black stones; do not buy black stones!

DIAMOND TESTERS AND U.V. (Ultra Violet light)

Some models of diamond tester have a built-in UV light, and this has led to the quite logical assumption that UV light can be used for testing diamonds. This is not true. There is absolutely no way you can distinguish diamond from non-diamond using UV light. The only useful thing to know is that diamonds fluoresce (glow) randomly.  So if you have a cluster ring or a diamond brooch and all the stones react in exactly the same way (whether they fluoresce or not) - they are probably not diamond; if some fluoresce and some don't...then they might be diamond...or they might not.

The information in this paragraph is for the gemmologist or professional diamond dealer, the average jeweller or antiques dealer does not need to know any of this:
UV light can give an indication of probability when comparing natural diamonds with synthetic diamonds (see 'Explanation' at the bottom of this section). For examining 'parcels' of diamonds you will need a UV lamp that provides long-wave AND a short-wave UV light. View the stones on a black background in a completely dark room (or a viewing cabinet). Natural colourless diamonds (of which about 40% fluoresce) usually fluoresce more under long-wave than under short-wave; some synthetic diamonds have just the reverse reaction, the fluorescence is weak (or nil) under long-wave, and  strong (or stronger) under short-wave. So if you buy loose diamonds, check each parcel under UV light to judge the probable mix of 'naturals' and 'synthetics'. But examining a diamond under a UV light tells you nothing. 

UV light can also be useful when grading a diamond for colour, because white diamonds that fluoresce under UV light also fluoresce under UV light present in daylight, and this can make the stone appear a better colour than it really is. Again, this information is for the gemmologist or professional diamond dealer, the average jeweller or antiques dealer does not need to know this.

Explanation: 'Synthetic' (also known as "lab-grown") does NOT mean 'imitation. A synthetic stone is grown in the laboratory to the same recipe found in nature  and the aim of the manufacturer is to make an end-product which is identical to its natural counterpart. Synthetic diamonds are diamonds (unlike, for instance, Cubic Zirconia or Moissanite which are not diamonds) - and most synthetic diamonds register DIAMOND on diamond testers...because they are diamond. It is extremely difficult to tell the difference between natural and synthetic diamonds, this requires a very special "synthetic diamond tester". 

MOISSANITE

Moissanite (read all about it) is a manmade stone (it doesn't exist in nature in a form that can be cut into gemstones*). It was only 'invented' in 1998, it is of no great value (though it does have a 'value' due to clever marketing), its only significance is that is registers 'diamond' on diamond testers. Moissanite does, to the non-expert, look remarkably like diamond - but it is not diamond it is Moissanite, i.e. Moissanite is not a 'type' of diamond, it is another stone altogether.

* It's found either as tiny black crystals of Silicon Carbide or as tiny green platelets. You can see pictures of Moissanite crystals here, they are less than 1mm in size and cannot be cut into gemstones. Part of the publicity about Moissanite is true: that the French chemist Henri Moissan (hence "Moissanite") discovered the mineral in a meteorite crater in Arizona in 1893. But the gemstone stems from a 1998 patent for "translucent silicon carbide of a single polytype that are grown in a furnace sublimation system" (i.e. it is grown in a furnace, it does not exist in nature) - and you will notice that, for the sake of the patent, it is known as "Silicon carbide gemstones" rather than the more romantic name "Moissanite". You've probably heard of Silicon Carbide under another name, the abrasive 'Carborundum'.

MOISSANITE TESTERS AND TYPE II DIAMONDS

Moissanite testers work by measuring electrical conductivity through the stone. Diamond is not electrically conductive, Moissanite is. However, there is a very rare type of diamond (Type II diamond) which has an unusual chemical composition (they do not contain nitrogen, they contains boron) and this makes the diamond electrically conductive, i.e. they register 'Moissanite' on both Moissanite testers and on 'multi' diamond testers. 

We had one of these diamonds and discovered that (with this particular diamond) some parts of the stone registered as Moissanite and some parts registered as Diamond - it turned out to be a synthetic (lab-grown) diamond. 

If you are not a diamond dealer handling thousands of diamonds, it's unlikely that you will ever see one of these. But, rare as these diamonds are, they are turning up at gem laboratories, sent in by anxious retailers following complaints by their customers (who have bought an expensive diamond only to find it registers 'Moissanite' on the tester).

MOISSANITE TESTERS AND UV (Ultra Violet light)

Unlike diamond testing, UV light does make a difference when testing a Moissanite on a Moissanite tester or on a combination (multi) tester.

The discovery was made by a gemmologist who worked out that, according to the laws of quantum physics, UV light should make a difference to electrical conductivity. He then took a deep breath and set about finding out just which exact wavelengths of UV light were required. To his amazement he found that any UV light worked. Moissanite testers that don't work on some 'difficult' Moissanites (rare as they are) work perfectly when the stone is exposed to UV light.

If you are buying a Moissanite tester, buy a UV light too, they really are not expensive (see how UV light works). If you are buying a combination diamond/Moissanite (multi) tester, there is a UV light built in to the tester; our Multi Experior is the only model that will enable you to shine the UV light on the stone whilst testing (other models give you the choice of testing the stone or using the UV light, but not both at the same time, which isn't really of any use).

DIAMOND TESTER OR MULTI TESTER?

A diamond tester (alternatively known as a diamond-only tester) will distinguish diamond from non-diamond with the exception of a manmade stone called Moissanite, which will register 'diamond'.

A multi tester will tell you if you have: diamond / not diamond / Moissanite (and, with the Multi Experior model, ruby and sapphire too).

I used to say that Moissanite wasn't common and that you were unlikely to come across it.

Moissanite is a manmade stone (read all about it), it was first made in the 1990s. I used to say that if you knew you had an old item that predated the 'invention' of Moissanite then the stones could not be Moissanite; that if you dealt in antique jewellery you would recognise genuine antiques that were too old to be set with Moissanite.

This is what I used to say.

However, as the years pass, Moissanite has become more common. It has now been around long enough for there to be lots of second hand Moissanite jewellery. It has now been around long enough to be passed down to the next generation, who may have no idea what the stone is. It has now been around long enough that most people (who are interested in jewellery) have actually heard of it. And, as time passes, manufacturers cut Moissanite in the 'old' style ('old-cut' or 'rose-cut') to imitate antiques.

For all of these reasons, I would now recommend a diamond/Moissanite (multi) tester rather than a diamond-only tester, so that you can distinguish diamond from Moissanite.

A  diamond-only tester (they register diamond on diamond and Moissanite) is a good cheap option if all you want to know is, "this stone is neither diamond nor Moissanite". 

WHICH MODEL?

DT-5 Quicktest diamond tester (diamond-only tester)

Advantages:

  • the chart on the back of the tester shows sizes of diamonds as circles actual-size, rather than a grid of figures.
  • we have completely re-written the instruction manual so there is no need to battle with a free translation from Cantonese or Japanese.
  • we've had these made so that they give correct readings on cold stones  (e.g. in outdoor markets and antiques fairs in the winter, and on large rubies and sapphires) - see the test results below. Other testers can't cope with cold stones, if it's cold enough everything shows up as diamond! 

Disadvantage:

  • making these work in the cold does have the side-effect of being 'sluggish' when it's warm, you often have to turn the sensitivity quite high to get it to work on diamonds. If you will never be working out in the cold it would be better to buy the next item (DT-CULTI).

DT-CULTI. (diamond-only tester)

This is the original Japanese DIAMOND SELECTOR II, not to be confused with those made by factories in China, which are copies. How do you tell which is which? See my guide to fake diamond testers.

Advantages:

  • for a relatively cheap diamond tester it isn't too bad, and it's far better than the many copies.  (We do sell one of the better copies, it's really cheap! - but the readings are not very reliable).

Disadvantages:

it must be used at room temperature or you will simply get wrong results.

MULTI-EXPERIOR, multi tester for diamond / Moissanite / Ruby-Sapphire tester.

As a compromise between best price and good performance (you'd have to spend twice as for the SAM, below) I'd recommend this one, and it's the only mult-tester that will also show ruby and sapphire.

CONCLUSION

To cover all possibilities, the MULTI-EXPERIOR will also distinguish Moissanite, which registers diamond on diamond testers. If you really have no idea about diamonds, you should be spending that extra little bit for one of these. This is the latest model, it also indicates ruby and sapphire. If you really want the absolute best, then it has to be the Presidium (multi) Adamas, and this is the one to buy if you will be working in extreme conditions, e.g. going to Africa to buy diamonds, or working in very cold conditions.

- if you already have a diamond tester, there's no need to buy a MULTI tester, there is a tester just for Moissanite.

If you are a dealer and are reasonably confident about identifying diamonds, and just want 'confirmation', then choose one of the following:

- if you ever work out in the cold or if you often come across large stones or if you intend to buy uncut crystals or if you are worried about false 'diamond' readings - go for the DT-5. This is my favourite, it has been designed especially for QUICKTEST, it minimises the chance of getting 'diamond' readings on non-diamonds. Note: there is a manmade stone, Moissanite, that will register as diamond on this model.

- if you are horrified at the idea of spending over £40.00 on a diamond tester but want something 'cheap' that is still of reasonable quality, or maybe you'll only be using it once or twice per year and can't justify spending much - then the DT-CULTI is probably OK. Note: there is a manmade stone, Moissanite, that will register as diamond on this model.

TEST RESULTS

Diamond testers work on 'heat'. Cold stones (typically large cold stones) will show up as diamond on a diamond tester, even if they are not diamond. 

The following charts show the test results when testing stones in the cold. Please read this is if you are a trader at fairs, markets and other outside venues. You  don't need to read any of this if you are only going to use the tester indoors in the warm, or if you are in a hot country.

When studying these charts, it is important to remember that the tests were carried out on some unusual stones in cold temperatures. If you are working in the warm and testing small stones, the testers will perform much better.

KEY

These are 'difficult' stones most likely to fool diamond testers, in reality you might not get to test stones as 'difficult' as our test-stones:

  • RUBY: a very large 'boule' of synthetic ruby, (20 ct by weight).
  • PHEN: a crystal of Phenakite (12 ct by weight) these are used to scam people into thinking they are buying uncut diamonds, they read 'diamond' on most diamond testers. Phenakite is not used as a gemstone, it is too soft and looks absolutely nothing like diamond. But the scammers target people who don't know this.
  • SAPP: a white sapphire (5pts on a spread gauge) bezel-set in silver, to make it 'cold'

CHART 1

Working indoors: what happens if a customer brings in a stone that's been out in the cold?  You need to wait for it to warm up.  But for how long?

Here, the stone temperature was 5° and the room temperature was 18° so the stones warmed up slowly. If the room temperature had been in the mid to high 20s, the stones would have warmed up quickly.

Of course, rather than just "waiting for a stone to warm up" you can help by warming it in your hand (one minute is enough for a small stone but a couple of minutes for a large stone).  

 

After 5mns left in the warm

 

After 10mns left in the warm

 

After 15mns left in the warm

 

After 20mns left in the warm

 

Ruby

Phen

Sapp

 

Ruby

Phen

Sapp

 

Ruby

Phen

Sapp

 

Ruby

Phen

Sapp

DIAMOND-ONLY TESTERS

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DT5 (Quicktest)

OK

OK

OK

 

OK

OK

OK

 

OK

OK

OK

 

OK

OK

OK

Diamond Selector (a good one)

fail

fail

fail

 

fail

fail

fail

 

fail

fail

OK

 

OK

fail

OK

Diamond Selector (a cheap one)

fail

fail

fail

 

fail

fail

fail

 

fail

fail

fail

 

fail

fail

OK

MULTI TESTERS

 

 

 

Adamas

fail

fail

OK

 

OK

fail

OK

 

OK

OK

OK

 

OK

OK

OK

Multi Experior

fail

fail

OK

 

OK

fail

OK

 

OK 

fail

OK

 

OK

OK

OK

Multi SAM

fail fail fail fail fail fail fail fail OK fail fail

CHART 2

Working outdoors: you can't let the stones warm up. Here, the air temperature was 2°, the stones had been outside in this temperature for one hour. The testers were warm (I shall assume the tester had been in the user's pocket).
Diamond testers are simply not designed to work at these low temperatures, so these were tough tests.

Tester model

Stone

 

Ruby

Phen

Sapp

DIAMOND-ONLY TESTERS

DT5 (Quicktest)

OK

OK

OK

Diamond Selector (a good one)

fail

fail

fail

Diamond Selector (a cheap one)

fail

fail

fail

MULTI TESTERS

Adamas

fail

fail

OK

Multi Experior

fail

fail

fail

Multi SAM fail fail fail

 

CHART 3

As above, air temperature 2°, but this time the testers were cold too (as if the user had left it on an outside market stall or was carrying it in a bag).
In these extreme conditions none of the testers coped with Phenakite and the Adamas failed to start up (the power light flashed for a minute then the power cut off). My advice: do not use a diamond tester in these conditions on any stone.

 

Stone

 

Ruby

Phen

Sapp

DIAMOND-ONLY TESTERS

DT5 (Quicktest)

OK

fail

OK

Diamond Selector
(a good one)

fail

fail

OK

Diamond Selector
(a cheap one)

fail

fail

fail

MULTI TESTERS

Adamas

Tester failed to warm up

Tester failed to warm up

Tester failed to warm up

Multi Experior

fail

fail

fail

Multi SAM fail fail fail

CHART 4

Room temperature 16° 

This could be the temperature of your shop on a cool day before the heating has had time to take effect. Warm small stones in your hand for a minute; warm large stones in your hand for two or three minutes - you will get better readings. 

 

Stone

 

Ruby

Phen

Sapp

DIAMOND-ONLY TESTERS

DT5 (Quicktest)

OK

fail

OK

Diamond Selector
(a good one)

fail

fail

OK

Diamond Selector
(a cheap one)

fail

fail

fail

MULTI TESTERS

Adamas

Fail

Fail

OK

Multi Experior

fail

fail

fail

Multi SAM fail fail fail