—Make a saturated solution of alum water, which means to dissolve as much alum in hot water as possible.
Lay the glass on a perfectly level table and pour on as much of the alum water as you can without its running off and let it cool slowly, when the alum will cover the glass with fine crystals. This is a good substitute for ground glass.
A cheap frosting for windows can be made by dissolving Epsom salts in hot water and then mixing it with a clear solution of gum arabic.
Substitutes for Glass.
—There are a number of substances that can be used instead of glass. In some cases a substitute is better than glass but generally they are used because they are cheaper.
Mica.
—This mineral, which is also but wrongly called isinglass, is found in Farther India; it is a silicate and can be split into thin sheets; in color it ranges from colorless to a jet black and from the transparent to the translucent. It is useful in many ways because it is fireproof.
Gelatine.
—Gelatine is obtained from the skins, hoofs and horns of animals. Isinglass is a nearly pure gelatine and is a white, tough, partly transparent substance which is obtained chiefly from the air-bladders of fish.
To make sheets of either gelatine, or isinglass, dissolve some of the finest glue, or isinglass—the latter is the best—in enough hot water so that it will form a flexible solid sheet when it is cold.