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: -

FIRST.

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

Paste

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.