This section is from the book "The Engineer's And Mechanic's Encyclopaedia", by Luke Hebert. Also available from Amazon: Engineer's And Mechanic's Encyclopaedia.
Glass prepared in imitation of gems. The basis of all artificial gems is a very hard and pure silica, obtained by melting pounded quartz with an alkali, with the addition of borax, nitre, and different metallic oxides, according to the intended colour of the gem. The materials should be of the purest kind, finely pulverized, well sifted, melted in crucibles of the best quality, and the fusion should be continued in a potter's furnace for twenty-four hours; the more tranquil and continued it is, the denser the paste, and the greater its beauty. The following are the ingredients, with their proportions, employed in the formation of some of the artificial gems. For what is called simply paste or strass, there are four different mixtures.
PASTES. | 1. | 2. | 3. | 4. |
Rock crystal . . . . . . . . . | .318 | .3170 | .300 | |
Minium . . . . . . . . . | .490 | .4855 | .565 | |
Pure potash . . . . . . . . . | .170 | .1770 | .105 | .054 |
Borax . . . . . . . . . . . . . | .021 | .0200 | .030 | |
Oxide of arsenic . . . . . . . | .001 | .0005 | ||
Litharge . . . . . . . . . . . . | .540 | |||
Ceruse . . . . . . . . . . . | .406 | |||
1.000 | 1 .0000 | 1 .000 | 1.000 |
For topaz, there are the two following methods: -
SECOND. | ||
Strass, (white paste) . . . . . . . . . . . | .95816 | .990 |
Glass of antimony . . . . . . . . . . . | .04089 | |
Purple of cassius . . . . . . . . . . . | .00095 | |
Oxide of iron . . . . . . . . . . . | .10 | |
1.00000 | 1.000 |
For ruby strass . . . . . . . . . . . . . . . . . . . . . . | .9755 |
Oxide of manganese . . | .0245 |
1.0000 |
For emerald, -
Strass, (white paste) . . . . . . . . . . . | .98743 | .9905 |
Green oxide of copper . . . . . . . . . .. | .01200 | |
Acetate of copper . . . . . . . . . . . | .0080 | |
Oxide of chromium . . . . . . . . . . . | .00057 | |
Peroxide of iron . . . . . . . . . . . | .0016 | |
1.00000 | 10000 |
For sapphire, -
Very white strass . . . . . . . . . . . | .9855 |
Oxide of cobalt . . . . . . . . . . . | .0145 |
1. 0000 |
For amethyst, | FIRST. | SECOND. |
Strass . . . . . . . . . . . . . . . . . . . . . . | .9870 | .9979 |
Oxide of manganese . . . . . . . . . . . | .0078 | .0022 |
Oxide of cobalt . . . . . . . . . . . | .0050 | .0001 |
Pueple of Cassius . . . . . . . . . . . | .0002 | |
1.0000 | 1.0000 |
For beryl, or aquamarine, | |
Strass . . . . . . . . . . . . . . . . . . . . . . | .9926 |
Glass of antimony . . . . . . . . . . . | .0070 |
Oxide of cobalt . . . . . . . . . . . | .0004 |
1.0000 |
For Syrian garnet, | |
Stass . . . . . . . . . . . . . . . . . . . . . . | .6630 |
Glass of antimony . . . . . . . . . . .. . . . . . | .3320 |
Purple of Cassius . . . . . . . . . . . . . . . . . | .0025 |
Oxide of manganese. . . . . . . . . . . . . . . . | .0025 |
1.0000 |
A mucilaginous preparation of wheaten flour, incorporated with water by boiling. Sometimes powdered resin is mixed with it; also gum arabic, size, etc, according to the peculiar wants of the artist or manufacturer. Alum is also considered to increase its cementing property.
 
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