GUIDE TO BUYING DIAMOND TESTERS

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If you intend going to Africa to buy 'cheap' diamonds, scroll down or click here before buying a diamond tester. Click here if you want to know about UV (Ultra Violet light) and testing diamonds.
Scroll down or click here for recommendations. Above these three 'click here' sections is the following article, by Raffi at Quicktest, originally published in the Antiques Trader newspaper:

I once walked into a local shop (it sold crafts and coins and the odd antique…and little bit of jewellery) and I said, "Hello Edward" (he didn't like being called "Ed") and I showed him one of our small battery-operated diamond testers. 

"Why would I want one of those?" he said, pointing to a handful of stone-set rings in his window.

Upon testing the first four rings this is what he found.  The first (labeled 'paste') was not diamond, the second (labeled 'diamond') was not diamond, the third (labeled 'diamond') was diamond, the fourth (labeled paste') was diamond - he bought the diamond tester.

Again and again customers at the fairs say, "If only I'd had one of these last week when I was buying a 'parcel' that contained stone-set jewellery!"  

We sell most of our diamond testers by mail and customers don't actually make a special point of writing to say how wonderful it is - but there are very few complaints.  In fact, the latest diamond testers are so reliable that virtually all complaints concern dogs ("The diamond tester worked fine until the dog chewed it") or tea ("I don't know WHY it doesn't work any more, do you think it might be because I spilt tea in it?") or the Bermuda Triangle ("I lost it").

Long ago a diamond tester was a big square box of electronics with a probe, you plugged it into the mains, waited two minutes for it to warm up, pressed the probe on the stone, waited for a reaction, and they cost over £200.00.

Today a diamond tester is small (the size of a tube of toothpaste), takes one standard battery, you wait twenty seconds for it to warm up, press the probe against the stone, and get a reading immediately.  And our best quality diamond tester costs just £65.00.

Many customers say, "How does it work?"  I never answer the question because they don't usually mean "How does it work?" they mean, "How do you work it?.  But in this article I shall answer both questions.

HOW DO YOU WORK A DIAMOND TESTER?

Switch on, hold it like a pen, wait for it to warm up (when the READY light shows), press the tip onto the stone, if the row of LED lights light up quickly (and there's a bleeping sound) then you have a diamond, if the lights don't move at all it is not diamond, if the lights move very slightly you probably have a ruby or sapphire (though a diamond tester is not designed as a ruby - sapphire tester).   There is also a safety feature that sounds an alarm if you accidentally touch the mount instead of the stone (which avoids false readings).

HOW DOES IT WORK?

Heat.  Or, to be more precise, Thermal Conductivity.  You may have seen traders 'testing' stones to see if they are paste or 'real' by touching the stone against the lip.  They are feeling (not very scientifically) for  "coldness."  Plastics (and maybe glass) feel warm-to-the-touch, many gemstones (probably) feel cold to the touch, as I say, it's not very scientific.  This relative coldness is what the tester is measuring, Thermal Conductivity.

ARE THERE DIFFERENT TYPES OF DIAMOND TESTER?

The most common type of diamond tester works on the principle of Thermal Conductivity.  There are two slight variations.  The cheaper models have two lights, one for Diamond and one for Not Diamond, the best model has a row of lights.  The advantage of the better model (row of lights) is that you can turn the sensitivity down if you are working in the cold (e.g. an early morning market), the cheaper model (two lights) will give false readings if it is cold. 

HOW RELIABLE ARE DIAMOND TESTERS? - WHAT ABOUT CUBIC ZIRCONIA AND MOISSANITE?

Of the two most common diamond simulates, Cubic Zirconia (including 'diamond-coated' Cubic Zirconia) presents no problem at all but Moissanite needs a special mention.  Moissanite is a purely synthetic stone (ie it is grown in laboratories by man, it does not exist in nature) and it registers as diamond on  diamond testers. This is an unfortunate fact of physics, that Moissanite has the same thermal properties as diamond.  So how do you tell Moissanite from diamond?  There is another  electronic tester, it looks (and operates) just like a diamond tester though it works on an entirely different principle.  Or there is a combined electronic tester for diamond and Moissanite. 

Do you need a diamond tester and a Moissanite tester?  Most people buy only the diamond tester; most people buy the diamond tester "just to start with" and some buy the Moissanite tester. Do you really need a Moissanite tester?  Here are two fascinating facts that might help you make your decision:

FACT 1.  Moissanite was first commercially grown ('invented') by man in 1995, so if you are quite certain that you are testing an antique ring (that hasn't been tampered with) then the stones won't be Moissanite. The origin, as a mineral (Silicon Carbide) found in meteorites, dates back to 1893, but this cannot be used as gemstones, quite contrary to the publicity that implies that a rare as-good-as-diamond gemstone comes from outer space!

FACT 2.  Moissanite hasn't quite taken off in the way that Cubic Zirconia did, probably because the smallest Moissanite costs several pounds whereas Cubic Zirconia costs a few pennies, so Moissanite isn't that common.  However, it's main purpose (it seems to me) is to fool antiques dealers, usually with a story about the item of jewellery having been in the family for many years.

So if you are trawling the fairs and boot sales and are happy that the items you see are genuinely old, you will probably be OK with just a diamond tester, but if you set up shop and advertiser that you buy jewellery you will attract the fraudsters, so make sure you have a Moissanite tester too.

Finally, there are testers that will test both diamond and Moissanite (i.e. one tester to test both), but they are quite fiddly to use, you are always better off with two separate machines, one for diamond and one for Moissanite. The main reason for the 'fiddly-ing" is that the machine first tests for diamond (thermal conductivity) then all the electronics re-set, then it carries out a second test, for Moissanite (electrical conductivity), and the electronics get confused and give wrong readings if you move the test-tip by a fraction of a millimetre during the test, or if you don't make firm contact with the stone, or if the stone isn't clean (you must clean it with a cotton wool bud and alcohol).

Whichever you choose, you will need good eyesight (good enough to see the tip of the tester and the very centre of the stone clearly) and a steady hand. I have watched many people who have neither of these attributes and will never, ever, be able to use a tester, at best they 'sometimes' get it to work.

ARE DIAMOND TESTERS FOOLPROOF - THE TALE OF A MAN WHO WAS FOOLED

Nothing is foolproof! Supposing, for instance, you bend the test-tip, fill the tester up with coffee, use a flat battery...

I recommend the type of tester with the row of lights that show how fast the machine is reacting, rather than two pre-set lights that tell you YES or NO. And by far the most reliable (to protect against fraud) is the latest QUICKTEST model DT-5. The following story is a warning to anyone who thinks that having a machine (any machine) is guaranteed to get them a bargain.

We sold a diamond tester to a man who went out to South 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. And 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.

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

Most importantly, 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. Well, perhaps if you go, in person, to the mines in the most war-torn parts of the world, traveling for days through barren land, braving road blocks and gunmen...

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 South 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 know 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.

All of this advice refers to the type of diamond tester (the type we recommend) that has a row of lights. The type with two lights to indicate YES or NO when buying diamonds is not suitable for buying rough (uncut) stones.

Also, these precautions do not apply in everyday dealing where the amounts of money involved are relatively small, there is no need to become paranoid. And I did sell a diamond tester to someone who was going to South 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!

DIAMONDS 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...but they might not.

UV light does, however, has some use for gemmologist because it 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 (this is the type we sell, this is the type on the diamond tester) AND a shortwave UV light (which we don't sell). View the stones on a black background in a completely dark room (or a special UV viewing cabinet). Natural colourless diamonds, when they fluoresce (about 40% do) usually fluoresce more under long-wave than they do under shortwave; some synthetic diamonds have just the reverse reaction, the fluorescence is weak (or nil) under long-wave, and  strong (or stronger) under shortwave. If, therefore, you buy loose diamonds it could be worthwhile checking each parcel under UV light to judge the probable mix of 'naturals' and 'synthetics'. But examining a diamond under UV light will tell 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 the UV that is present in daylight, and this can make the stone appear a better colour than it really is, so you may wish to downgrade it by one or two colours. Again, this is for the gemmologist or professional diamond dealer, the average jeweller or antiques dealer does not need to know any of this.

EXPLANATION: 'Synthetic' 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 diamond IS diamond (unlike, for instance, Cubic Zirconia or Moissanite which are not diamond) - and synthetic diamond registers DIAMOND on diamond testers...because it IS diamond.

RECOMMENDATIONS

Diamond Testers

Our own brand is imported by us, and we helped design it - it is called model DT-5 on page 20 of our current (Winter 2009 - Spring 2010) mail order catalogue. It is based on previous models that we have been selling for many years, but 'tweaked' to our specification. The main change is that we've made it less sensitive so that it doesn't give a false 'diamond' reading on large rubies and sapphires and very cold stones. Not being able to cope with large / cold stones seems to be a fault caused by the Chinese / Japanese idea of 'cold', when they design these testers they simply have no conception that someone might use one at an outside market in the winter and test stones that have been in sub-zero temperatures (they will all register 'diamond'!); and when they calibrate them for 'cool' temperatures they test stones at about 15 degrees not 1 degree.

We have made other changes too, we have completely re-written the instrcution manual so there is no need to battle with a free translation from Cantonese of Japanese. We have re-labelled the controls, the knob is now correctly labelled 'Sensitivity' rather than than the confusing 'Volume'. The new labelling also makes it clearer as to which lights indicate 'diamond', and also extend the number of segments from 8 to 9. The chart on the back of the tester shows sizes of diamonds as circles actual-size, rather than listing sizes in 'points' and expecting the user to refer to a diamond gauge. The price is £65.00.

If you have used a tester of the 'original' design, you will notice that our model isn't as sensitve, the lights don't shoot up as dramatically, but we have done this on purpose, to avoid getting false 'diamond' readings.

The second model (model DT-4) is the original manufacturer's design, a tiny bit over-sensitive, bad if you're testing large rubies and sapphires but good if you deal mainly in very small diamonds, not suitable for testing cold stones but fine if you work indoors in the warm and ensure stones are at room temperature. Other features: it's just a bit smaller than the standard DT-5 above; you have the option of using mains power if you buy a suitable power supply (personally, I wouldn't bother); it has a nice rubberised finish; it includes a UV light. The price is £70.00.

For all those who think £65.00 and £70.00 is a huge amount to pay...well, I do have a random selection for £30.00, I call them 'eBay quality', I will guarantee them for 14 days. You will, of course, always get them to register diamond or not diamond - but you will never be 100% certain if the result is correct. And for £30.00 we don't give any help if you don't understand the instructions or 'don't feel comfortable' with the readings - just like on eBay!

Moissanite (and combined Moissanite / Diamond testers)

The Moissantie testers are quite reliable, the combined testers tend to be fiddly to use (see above).