it is a sensitive piece of laboratory equipment, it must be kept clean and dry, the sensor must be kept dust-free, it must not be bumped in and out of bags or used on damp outside market stalls NO REACTION, if it's low thermal thermal conductivity (those that never give a reading on a standard diamond tester) - it could be anything, but it's not diamond

if you are quite happy to work slowly and carefully in laboratory-clean conditions but you must have a machine that will positively identify any stone: such a tester does not exist This has both an anlogue meter operated by a probe ('thermal' tester) and a digital meter (for refractive index/reflectivity). There are pros and cons of both types. In summary, the digital meter will test 40 stones, but it will only test loose stones (not stones set in jewellery) and you have to be careful and clean to get a correct reading; the analogue meter is very easy to use (on loose stones and on set stones) but only tests 17 stones, most of which have overlapping readings: nearly as easy as the 'Standard' Presidium, above - it has more settings, you can narrow the results by selecting the colour of the stone you are testing As the leaders in diamond and gemstone testing, Presidium gem testers are a must for the jewellery maker. Provide accurate and reliable results instantly when working with diamonds and other gemstones. Here is its full list of gemstones the Presidium handheld gem tester will detect (but please study the chart above, so see how the readings overlap!) -For the non-expert: if it has any colour (e.g. the tiniest slightest yellow tint) you won't get an accurate reading. It takes an expert to colour-grade a stone, to the non-expert Colour Grade D will look exactly the same as Colour Grade J. For the professional jeweller: if you work at a shop counter and don't understand this, please ask your diamond expert to colour-grade the stone for you. if you understand the limitations of gem testers but there really is no way you have time to keep the tester meticulously clean and clean every stone before every test, and you cannot guarantee that it will never be bumped or dropped or get dusty or damp. Reflectivity / Refractive Index testers are optical not thermal (so they work at any temperature), they help identify many dozens of stones. not ideal for buying at outdoor venues when it's cold, the tester must be used at room temperature.

So if you are testing a large stone and there's a slight reaction with the lights, you know it cannot be diamond, even if the lights tip into the DIAMOND zone (test it again, turn the sensitivity right down). Opt for the latest model: technology is constantly changing everywhere, and that’s the same for diamond testing detectors as well. The latest models combine heat and electricity testing for the greatest accuracy. The Presidium ARI is an essential tool for the experienced jeweller and professional diamond dealer, it is for testing known diamonds. However, it is worth mentioning that a diamond tester will not help identify if a diamond is created or natural. Other methods are used to distinguish between them. These methods include detecting colour zoning, strain patterns, inclusions, fluorescence, etc. Get a friend or colleague to use the tester. Get two or three friends or colleagues to use the tester. As each one does this, either leave the room or keep your mouth firmly shut, don't give them any clues, let them work it out for themselves. Very often if it works when they use it, see what it is that they are doing different.

Whenever anyone asks if a tester is "100% guaranteed to identify all diamonds" I take a deep breath. There are always always always exceptions. And these apply to all brands of diamond / Moissanite / multi testers.