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Diamond Testing

Thermal Diamond Tester

Diamond Testers - How They Work
Sometimes one needs to get a diamond tested to ensure it is, in fact a real diamond. Artificial and synthetic diamonds are so close to the original nowadays that in order to be able to spot the difference one needs to get a diamond tester to check the diamond to see if it is genuine. Some years ago, before synthetic diamonds were produced a diamond tester called a thermal detector was used. This tester has a metal tip which is heated to a high degree and then the tip is applied to the diamond being checked. A transfer of heat occurs and if the read back from the diamond to the tester matches then you could say you have a real diamond on your hands. However this is not such a good test these days as a synthetic diamond will show the same readout as a genuine diamond so more sophisticated tests are used these days to overcome this problem. Diamond simulants, or synthetics usually come as synthetic cubic zirconia, synthetic strontium titanate, YAG (yttrium aluminium garnet) and GGG (gadolinium gallium garnet).

Currently there are four types of diamond tester used these days.

Ceres Diamond Tester, the Rayner Diamond Tester, the Diamond Pen, used by the GIA and t Fluorescence Diamond Testing.

Ceres Diamond Testing
The Ceres Diamond tester works on the principle that diamonds conduct heat at a high thermal conductivity. No diamond simulants will conduct heat so well and are typically very poor conductors of heat. So by applying this principle one can easily sort out the genuine diamond from the simulant.

In use it needs to be apply correctly as, of course, metals such as silver, gold and platinum will conduct heat and so if you touch the ring a diamond is set in you will get a high reading. Also moissanite's thermal conductivity is similar to diamond so one should conduct a moissanite test also to a diamond one has tested to be sure it is not a moissanite.

The Ceres will, however spot cubic zirconium as the thermal conductivity is very different to a genuine diamond.

It is a very delicate instrument and should be used with care to ensure you do not damage the tip and also get an accurate reading.

Rayner Diamond Tester
The Rayner Diamond Tester is a more expensive instrument and designed for the professional diamond dealer or jeweller. The Rayner works similar to the Ceres but is more exact. One needs to be in the profession in order to obtain a Rayner Diamond tester.

Diamond Pen
The Gemmological Institute of America (GIA) use a diamond tester they have developed themselves. This does not work on the thermal principle but on the property of non absorption of a special liquid when applied to a diamond. A special pen is used rather like a fountain pen and a drop of a greasy type liquid is placed by the pen on the diamond surface. On a diamond it will leave a visible mark but on any other kind of stone the liquid beads up and does not leave any marks.

Fluorescence Diamond Testing
A Fluorescence diamond tester will test the fluorescence of a diamond. Under long-wave ultra-violet light, diamonds will show a very varied degree of fluorescence since all diamonds have a fluorescence level measured from one to five and each falls somewhere on that scale but as each stone is different doing a comparison it is easy to see. Synthetic diamonds all have the same florescence so can be clearly seen to be synthetic. Under X-rays, almost all diamonds show a blue fluorescence and a brief exposure on film will show diamonds to be far more transparent to X-rays than any other stone. This test, however, although considered a decisive test, should be done in conjunction with either the thermal or Pen method also.

Immersion Contrast Method
One can also use the Immersion Contrast Method. When light is placed over simulant stones such as Strontium titanate, YAG, GGG and CZ, for example and immersed in di-iodomethane (methylene iodide; a high density liquid with a refractive index of 1.742) or Refractometer contact fluid (RI 1.81), the different stones show differing patterns. All except strontium titanate will show a dark ring diminishing in width as their refractive index approaches near to that of the liquid. This is a definite visual indication of differentiation between diamond and its simulant.

So the above shows how the principle diamond testers work. It is important to ensure that one's diamonds are the real McCoy and this can easily be done by any of the Diamond Testers above.


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