554 REPORT OF NATIONAL MUSEUM, 1900. 



These proportions admit of considerable variation. For example, 

 borate and chloride of silver are added to produce topaz yellow; or the 

 first mixture i>-iven for topaz is, after fusion, mixed with 8 parts of 

 strass and re-fused for thirt}' hours and used as a ru))y glass. The 

 ruby composition is colorless and onl}^ acquires its color upon re-fusion, 

 the de})th of color l)eino- varied ])y the addition of compounds of tin. 



These imitations can, as a rule, be readily detected. They are defi- 

 cient in hardness and A-^ield readih^ to the file. Further, they aie liable 

 to tarnish in impure air, are not pleochroic as the majority of colored 

 gems are, and under the magnifying glass they show the many lines, 

 striae, and bubbles characteristic of fused glassy masses. Final Iv they 

 differ in specific gravity from the gems they represent. 



Instead of a purely imitative preparation being used, what is known 

 as a "doublet" may be constructed.' The doublet is made up of the 

 table and crown of a genuine stone, usually somewhat off-colored, 

 cemented to a pavilion made of a paste having the approved color, 

 thus giving the valueless crown the appearance of a fine stone. The 

 doublet usually betrays itself by the softness of its pavilion. To avoid 

 this the "triplet" has been devised. This consists of a crown and 

 pavilion made usually from a pale or off-colored stone with a thin layer 

 of colored glass at the girdle. Here the hardness test will be found 

 wanting and the magnifying glass and specific gravit}' test nmst be 

 used. The glass usualh" distinguishes the composite nature of the 

 triplet, and if soaked in alcohol, carbon bisulphide, or ether, the fraud 

 will usually betray itself by falling to pieces. 



The manufacture of imitation pearls by coating the inner surfaces 

 of glass beads with a preparation made from the scales of certain fishes 

 is extensively carried on as a home industry in the glass-iuaking centers 

 of Europe. The manufacture of the fish-scale extract, as carried on in 

 Thuringia, is substantially as follows: Four to five pounds of l)leak scales 

 (obtained from the Baltic) are washed in fresh water to remove dirt; they 

 are then churned for about two hours in six quarts of cold fresh wate;r 

 and the whole subjected to pressure in a linen hag. 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. AVhen 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 has the 

 consistency of butter. For use, th(> preparation is mixed, in small 

 quantities, with a hot aqueous solution of gelatin to which a small 

 amount of alcohol has been added. Colored pearls are made from it 

 by the addition of the desired coal-tar dyestufi'. 



