The function of the microscope is to enlarge objects so as to make them more unmistakably descriptive to the human eye. Its use in science is unlimited, and to the gemologist the microscope is more foremost than any other instrument. This is because one of the biggest problems in modern jewelry is the detection of artificial and imitation stones, and without a microscope the task would be roughly impossible.
The detection of imitation stones covers a vast field and the following lines serve only as an introduction. Three out of four of the most valued gem stones can be produced synthetically in the laboratory. These are the ruby, the sapphire, and the emerald. Needless to say, the distinction in value in the middle of a natural and artificial stone is enormous, and it is therefore of most point to the jeweler that he can be sure they can be effectively distinguished from each other.
Microscope
Synthetic rubies made by the flame-fusion process are in all their corporal properties roughly identical with the natural stone. Chemically, both are crystalline aluminum oxide. The red color is in both cases produced by minute quantities of chromic oxide, and if artificial and natural rubies are tested for their exact gravity, refractive index, and absorption spectra, the same results occur in both cases. Yet, if they are placed under a microscope, a marked distinction in the middle of the two is found. What then are these internal telltale features that will enable us to distinguish the real from the synthetic?
Fine curved lines are immediately noticeable that are rather like the grooves of a phonograph narrative and run through the stone. There are also some black spots interspersed irregularly throughout the gem. The curved lines are known as increase lines, and they are produced during the formation of the artificial boule and are a distinct sign that the stone is synthetic. The black spots characterize tiny bubbles of gas, and these, too, were included in the boule during its formation. Gas bubbles and curved increase lines are therefore typical characteristics of artificial corundum.
But, what does the inside of natural corundum look like under the microscope? Again, there are the curved increase lines in the artificial stone, but, in the natural one, the increase lines are right and set at exact angles. This latter feature is an foremost characteristic of most natural mineral crystals. The microscope can supply all-important clues in the identification of rubies and sapphires.
A gem stone that may set an even bigger problem is the emerald. In this case, artificial stones are internally also remarkably similar to the natural ones. Fortunately, Chatham's artificial emeralds do have a lower exact gravity and refractive index than the natural stones, but it is not always possible, if a stone is set in a piece of jewelry, to apply these tests. Here the microscope is useful again.
Natural emerald possesses cer¬tain internal features called inclusions. Some of them take the form of spiky cavities filled with tiny mineral crystals and gas bubbles. Indeed, they are so typical that they can be connected with exact mining localities and thus form an foremost guide to the origin of some emeralds. Chatham's artificial emeralds also possess extra inclusions, and under the micro¬scope, these look rather like a fine pattern of lace. They unmistakably consist of minute interweaving channels filled with liquid and thus are very different in character from the inclusions of the natural emeralds.
A easy magnifying glass that enlarges ten times can also be a requisite aid in the identification of some gem stones. Thus, a colorless zircon might well be confused with a real diamond, but if both are determined examined with a hand lens by finding through the top of the stone at the rear facets, everything at the back of the zircon will appear double, thus revealing its strong light-splitting property.
Since a diamond belongs to the cubic crystal system, letting light rays pass through without splitting them, the duplicate image will not be shown by it. This is one easy test that immediately distinguishes in the middle of these two gem stones. There is one direction along the so-called optic axis of a double-refractive stone where the light rays are not split and the doubling ensue cannot be seen. It is therefore wise to tilt the gem a minute when examining it with a lens to insure that the optic axis does not lie at right angles to the table facet.
Gemstone Microscope and Its Usage
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