Gem Tester?

Question

Does any of the Gem testers you can buy online or from stores work good? Are they reliable?

Answer 1

There are a number of testing instruments available on the net which fall into different categories. Firstly you must understand that there is NO single machine that you can put a stone on and it will tell you what that stone is - no matter what the advertising may say.
The first type of instrument is the simple diamond detector which is based on the rate of heat dispersion. They give a simple yes or no answer and are quite reliable however some synthetics can fool them so additional tests may be needed.
The second type consists of various reflectometers. These are electronic testers that rely on the way light is reflected from the surface of a stone. They have many draw backs the major one being that the surface being tested must have a perfect polish and be absolutely clean (not even a finger mark). These machines are often fitted with scales that give gemstone names but these are ONLY a guide and are not absolute answers, some give the results as refractive index numbers. There are many more problems which I will not list in a short answer. On the whole I regard these instruments as costly guessing machines. If you ever find one in a professional testing lab it will be stuck in a cupboard covered in dust.
The third group of testing tools are optical instruments, the most common being the refractometer. This will not only give a direct reading of the refractive index but allow you to determine optical sign and birefringence as well as an indication of dispersion. Next to the microscope this is the gemmologist's most useful tool. The spectroscope is also greatly used but requires knowledge and skill to use properly which takes time and practice to learn.
As I said there is no single instrument to give you a definitive answer. In my opinion the best method is to take a proper course on gemmology. Machines can give you figures but those numbers have to be interpreted and added to the information you have gained from examining the stone by eye, only then can you make an identification that will be any where near reliable.