IMITATION GEMS. Imitation gems may be di vided into two classes—namely, mineral sub stitutes and doublets, and gems made from sub stances treated by chemical means. The first class includes quartz, white Brazilian topaz, and the colorless varieties of beryl, emerald, sapphire, and zircon, which have been sold as diamonds. Colored varieties of quartz are frequently sub stituted for other gems; thus, the yellow varie ties, as cairngorm and citrine, are sold as topaz, and the purple varieties of quartz as the Oriental amethyst: The application of heat to certain gems, such as topaz and sapphire, frequently renders them colorless, and increases their bril liancy, in consequence of which they are cut and sold as imitation diamonds. Doublets are thin plates of a genuine gem attached to a valueless backing by means of a thin layer of gum mastic. Those imitation gems that are made by chemical processes are generally a special variety of glass known as paste, or strass, which consists of pure powdered quartz (preferably rock crys tal) 38.2 parts, red lead 53.3 parts, and dry potassium carbonate 7.8 parts. These propor tions admit of considerable variation, and ar senious oxide, borax, potassiui nitrate, alu minum hydroxide, and calcium carbonate are also frequently added. The ingredients are pow dered separately, carefully mixed, and heated in a sand crucible. The heat is gradually raised to fusion, and is maintained and carefully regulated at that temperature for about thirty hours, after which it is gradually lowered. The value of the product depends chiefly on the regularity of the temperature, the intimacy of the previous admix ture, and the slowness of cooling, and is much increased by prolonged fusion.
This glass forms the basis of nearly all of the imitation gems, and the imitation diamonds are cut directly from it. The required tint for the colored gems is imparted by the solution in the paste of certain metallic oxides and other sub stances, as is shown in the following formulas: Amethyst, paste 1000 parts, glass of antimony 8 parts, cobalt oxide 5 parts, purple of Cassius 0.2 part; beryl, paste 1000 parts, glass of anti mony, 7 parts, and cobalt oxide 0.4 part; car buncle, paste 1000 parts, glass of antimony 500 parts, purple of Cassius 4 parts, and manganese dioxide 4 parts; emerald, paste 1000 parts, cop per oxide 8 parts, and chromium oxide 0.2 part; garnet, paste 1000 parts, with variable propor tions of purple of Cassius; ruby, paste 1000 parts. glass of antimony 40 parts, purple of Cas
sius 1 part, and gold 1 part; sapphire, paste 1000 parts, cobalt oxide 14 to 25 parts; topaz, paste 1000 parts, glass of antimony 40 parts, and purple of Cassius I part. The temperature at which these mixtures are fused, and the time occupied in fusion, naturally affect the product, and the proportion of the colorless ingredients also varies considerably. The manufacture of these imitation gems is an important industry in Switzerland and in various parts of France and Germany. Agate, carnelian, chalcedony, and onyx, for making jewelry and for engraving, have been artificially stained at Oberstein and elsewhere in Germany. The stones are soaked in oil or other organic liquid, and boiled in strong sulphuric acid. The organic matter ab sorbed by the stone is thus carbonized, and a black color is produced. A red color may be ob tained by soaking the stone in a solution of fer rous sulphate, and a deep blue color results by afterwards soaking in a solution of potassium ferricyanide.
The manufacture of imitation pearls is an im portant industry. The pearls are made by coat ing the inner surfaces of glass beads with a preparation made from the scales of certain fishes. This extract is prepared as follows: Sev eral pounds of scales are washed in fresh water to remove dirt, and they are then churned for several hours in cold fresh water, and the mass subjected to pressure in a linen bag. The silvery, lustrous runnings are caught and set aside, and the operation repeated until the scales have lost their silvery appearance. The runnings, to which a little ammonia has been added, are put aside to clarify, care being taken to prevent putrefaction. The sediment is washed repeatedly with fresh water and left to settle; when the washings are quite clear the lustrous sediment is bottled with its own volume of alcohol, shaken, and allowed to settle. The alcohol is then decanted off, and the operation repeated until the sediment has lost its water and is of the consistency of butter. For use, the preparation is mixed in small quan tities with a hot aqueous solution of gelatin, o which a small quantity of alcohol has been added. In the manufacture of colored pearls the desired shade is obtained by the addition of some suit able coal-tar dyestuff.