HOW TO TELL SCIENTIFIC STONES FROM NATURAL GEMS

It should be said first that the only true scientific or synthetic stones on the market are those having the composition and properties of corundum, that is to say, the ruby and the several color varieties of sapphire, as blue, pink, yellow, and white. There is also a greenish stone that appears reddish by artificial light, which is called scientific alexandrite but which has, however, the composition and properties of the corundum gems rather than those of true alexandrite. All so-called “scientific emeralds” have proved to be either of paste of one sort or another, or else triplets having a top and a back of some inexpensive but hard stone of pale color, and a central slice of deep green glass, the three pieces being cemented together so skillfully that the junctions frequently escape any but a very careful examination with a lens.

ALL SCIENTIFIC STONES ARE CORUNDUM GEMS. Now the fact that all true scientific stones are corundum gems makes their determination fairly simple on the following basis: Among the considerable number of corundum gems of nature, whether ruby or sapphire of various colors, there is seldom found one that is entirely free from defects. Almost always, even in what are regarded as fine specimens, one will easily find with a glass, defects in the crystallization. Moreover these defects are characteristic of the corundum gems.

The scientific corundum gems, however, never have these specific defects. Hence the surest and simplest way of distinguishing between the two kinds of stones is to acquaint oneself with the typical defects of natural corundum gems, and then to look for such defects in any specimen of ruby or sapphire that is in question.

While a description of some of the most common of the typical defects of rubies and sapphires is to follow, the jeweler, who may not yet be familiar with them by actual experience, owes it to himself and to his customers to acquaint himself at first hand with the natural defects of such material, which he is always in a position to do through the courtesy of representatives of houses dealing in precious stones, if he himself does not carry such material in stock.

TYPICAL DEFECTS OF NATURAL CORUNDUM GEMS. Perhaps the most common of the defects of natural corundum gems is the peculiar appearance known as “silk.” This is best seen when a strong light is allowed to stream through the stone at right angles to the observer’s line of sight. Sets of fine, straight, parallel lines will be seen, and these will frequently meet other sets of similar lines at an angle of 120 degrees (like the angle at which the sides of a regular hexagon meet) or the lines may cross each other at that angle or at an angle of 60 degrees (the supplement of 120 degrees). Such straight parallel lines are never seen in scientific stones, and their presence may be taken to indicate positively that the stone having them is a natural stone. In fine specimens of natural ruby or sapphire such lines will be few and difficult to find, but in some position or other they will usually be found if the search is even as careful as that which one would habitually employ in looking for defects in a diamond. In the vast majority of cases no such careful search will be required to locate “silk” in natural rubies, and if a stone that is apparently a ruby is free from such defects it is almost a foregone conclusion it is a scientific stone.

Another common type of defect in corundum gems is the occurrence of patches of milky cloudiness within the material. A little actual acquaintance with the appearance of this sort of defect in natural stones will make it easy to distinguish from the occasional cloudiness found in scientific stones, which latter cloudiness is due to the presence of swarms of minute gas bubbles. These tiny bubbles can be seen under a high power lens, and this suggests a third feature that may be used to tell whether one has a natural stone or not.

Natural rubies and sapphires, like scientific ones, frequently contain bubbles, but these are always angular in the natural stones, while those of the scientific stones are generally round or rounding, never angular.

To sum up the suggestions already presented it may be said that, since natural and scientific corundum gems are composed of essentially the same material, and have identically the same physical and chemical properties, and frequently very closely resemble each other in color, it is necessary to have recourse to some other means of distinguishing between them. The best and simplest means for those who are acquainted with the structural defects common to natural corundum gems is to seek for such defects in any specimen that is in question, and if no such defects can be found, to be very sceptical as to the naturalness of the specimen, inasmuch as perfect corundum gems are very rare in nature, and when of fine color command exceedingly high prices. No jeweler can afford to risk his reputation for knowledge and for integrity by selling as a natural stone any gem which does not possess the minor defects common to practically all corundum gems.

STRUCTURAL DEFECTS OF SCIENTIFIC STONES. So far our tests have been mostly negative. It was said, however, that spherical bubbles sometimes appear in scientific gems. Another characteristic structural defect of practically every scientific gem may be utilized to distinguish them. As is well known, the rough material is formed in boules or pear-shaped drops under an inverted blowpipe. The powdered material is fed in with one of the gases and passes through the flame, melting as it goes, and then accumulating and crystallizing below as a boule. The top or head of this boule is rounding from the start, and hence the successive layers of material gather in thin curved zones. The color and structure of these successive zones are not perfectly uniform, hence when cut stones are made from the boules these curving parallel layers may be seen within by the use of a good lens, especially if the cut stone is held in a strong crossing light, as was suggested when directions were given above as to the best way to look for “silk” in a natural stone.

Owing to the shape of a well cut stone it is sometimes difficult to get light through the material, yet by turning the stone repeatedly, some position will be found in which the curving parallel striae can be seen. They are easily seen in scientific ruby, less easily in dark blue sapphire, but still they can be found on close search. In the light colored stones and in white sapphire, the difficulty is greater, as there are no color variations in the latter case. However, the value of white sapphire is so slight, whether natural or artificial, that it is a matter of but little moment, and what has already been said as to natural defects, applies to white sapphire as well as to the colored varieties, and absolutely clear and perfect natural white sapphire is rare.

One more distinguishing mark of the scientific stones may be added to give full measure to the scheme of separation, that no one need be deceived.

The surface finish of the scientific stones is rarely as good as that of the natural material and it appears to be more difficult to produce a good polish on scientific stones than on natural ones. The degree of hardness of the scientific stones seems to be slightly variable in different parts of the same piece so that the polishing material removes the surface material unequally, leaving minute streaky marks on the surfaces of the facets. Possibly this condition might be remedied by skillful treatment, but hardly at the price obtainable for the product, so that a close study of the surface finish will sometimes help in distinguishing between natural and artificial material. Any fine specimen of natural ruby or sapphire will have usually received very expert treatment and a splendid surface finish.

In conclusion, then, the points to be remembered in determining the origin of corundum gems are four in number.

1. Expect to find natural defects, such as “silk” or cloudy patches, or angular bubbles in all natural stones.

2. If bubbles are present in artificial material they will be round or rounding.

3. Artificial material will always have curving parallel striae within it.

4. The surface finish of artificial material is seldom or never equal to that of natural material.

It ought not to be necessary to add that material from either source may be cut to any shape, and that artificial rubies may be seen in most Oriental garb, hence all specimens should have applied to them the above tests regardless of the seeming antiquity of their cut or of their alleged pedigree.