The Book of Talismans, Amulets and Zodiacal Gems [1922] by William Thomas and Kate PavittREAL AND ARTIFICIAL GEMS AND HOW TO TEST AND SELECT THEM
The following notes are written in the hope that they may put readers upon their guard against some common deceptions and prevent disappointment which with a little knowledge can be avoided.
The qualities which make gems valuable are beauty of colour, brilliancy or fire, and hardness, in which they excel all other substances known.
A large variety of coloured stones come from Ceylon, and many tourists and travellers buy stones there in the hope of securing bargains, a hope that in the majority of cases does not materialise. Dealers in gems are amongst the shrewdest of mankind, and from continually handling and examining stones become wonderfully keen in judging them from their appearance and feel, and are very seldom mistaken in distinguishing the real from the imitation, and no novice will get the better of them in a deal, so that intending purchasers who have no practical experience of gems are advised to buy from established firms with a reputation to lose, or on the advice of an expert, rather than rely upon their own judgment.
Before the full beauty of a stone can be appreciated it has to be cut and polished, either with facets, or in the form known as cabochon. Practically all transparent stones are cut with facets, the best and most popular form being the "brilliant" cut (as shown in Illustration No. 1 of the Frontispiece) which has been. found so effective with diamonds that the term "brilliant" has become the recognised name for a diamond cut in this manner.
With oblong stones "trap" cutting is followed, Emeralds being the principal stones cut in this fashion (as shown in No. 4 of Frontispiece). "Rose" cutting is the form generally adopted with very small diamonds nowadays, although it is a much older form than the brilliant, and large antique stones are to be found cut in this fashion, culminating in a point formed by six triangular facets in place of the table of the brilliant. Semi-transparent and opaque stones, such as Moonstones, Opals, Agates, Turquoises, and Cornelians are usually cut en cabochon (as shown in the stones illustrated in Nos. 3, 6, and 7 of the Frontispiece), and Amethysts, Rubies, Emeralds, and Sapphires are also frequently cut in this fashion.
For years past scientists have been experimenting in the manufacture of precious stones, and with so much success that reconstructed stones have been put on the market and are now fairly universally used. These stones are made up from fragments of small genuine stones which are fused together by a continuous and very powerful flame directed on the mass whilst it is kept in motion, resulting in a solid lump that can be cut and polished in the same way as the natural mineral. This has been very successfully done with Rubies, some having been produced which passed every test save that of the microscope, which revealed numerous minute bubbles of a rounded shape invisible to the naked eye, and in greater quantities than would be found in the natural stones wherein the bubbles are more rectangular in shape. These Rubies, and also reconstructed Sapphires and Emeralds, are on sale everywhere at the present time, so that intending buyers of precious stones should ask their jewellers to guarantee that they are buying natural and not reconstructed stones.
All transparent gems may be roughly divided into two classes, singly and doubly refracting, a ray of light passing through being refracted or thrown back according to the nature of the stone. If, therefore, a lighted candle is placed in a darkened corner of a room and is looked at through a stone focussed between the eye and the candle, if the stone is a doubly refracting one two images of the flame will appear, and if it is singly refracting, one only will be seen. Stones that are doubly refractive are Ruby, Beryl, Topaz, Sapphire, Emerald, Tourmaline, Peridot, Chrysolite, Aquamarine, Amethyst, Jargoon, Zircon, and Crystal. Singly refracting stones are Diamonds, Spinels, and Garnets; glass also is singly refracting.
One of the simplest and most effective methods of testing the genuineness of a gem is to try if it is affected by filing with a small jeweller's file; care must be taken, however, in its use, as the facets of even some of the hardest stones are easily chipped. If the file scratches the stone it may be taken to be glass, or composition.
Combination stones, known as "Doublets," are frequently sold as genuine stones; in these the top part is made of the real stone and the lower part of crystal, glass, or composition, so that for their detection the bottom part as well as the top must be tried with the file. "Triplets" are another form of deception. In this case the tops and bottoms of the stones are genuine and the centre part is imitation: To detect this the gem should be held in a small pair of forceps, or corn tongs, in a cup of clear water, when the different parts of the stone will be plainly seen.
White Sapphires, Jargoons, and Aquamarines are sometimes mistaken for diamonds; but the White Sapphire will frequently have a suggestion of cloudiness, and the Jargoon or Zircon, though very hard, is brittle and chips easily, soon showing signs of wear. White Aquamarines usually have a slight bluish or greenish tint. White Topazes and Rock Crystal are not so brilliant and full of life as the other white stones, and all these are doubly refracting, whilst the Diamond is single.
Imitation Sapphires are as a rule harsher in colour than the real stone, which is soft and rich in the quality of its colour.
Pearls are imitated with great skill, and are difficult to detect. They are usually lighter than the real Pearls, and if drilled the holes are seldom as small, and show marks of chipping and breaking round the edges. Pearls lose their lustre and deteriorate with age and the effect of gas and acids, and should be carefully wiped with a clean cloth after being worn, and in order to retain their brilliancy should be kept in dry magnesia.
Amber is imitated with glass and various compositions, glass being colder and harder to the touch and heavier than real Amber; whilst celluloid, which is frequently used, if rubbed briskly on a piece of cloth, will give off a noticeable odour of camphor which is largely used in its composition.
Opals and Turquoises, being porous, are affected by potash which is commonly used in the manufacture of soap, and also by oily or greasy substances; they should also be kept from contact with scent, as the spirit used in its. manufacture will very soon spoil the colour of Turquoises.
In conclusion, to ascertain if a transparent stone has any flaws it should be breathed upon until its lustre is temporarily dimmed, when any flaws or imperfections that exist can readily be seen.
Source:
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