Page:Popular Science Monthly Volume 35.djvu/31

Rh added immensely to the brilliancy of modern designs, and have been particularly effective when introduced as a setting or framework to a picture-window. They are imported for the most part from Germany. The greater part of the flat glass used, however, is made in the immediate neighborhood of New York, under the direct supervision of the art-workers who are to utilize it. I had recently the pleasure of going through such a factory in Brooklyn, probably the largest of the kind in this country, and it was a veritable chromatic treat to visit the store-rooms, for some five hundred different color combinations were recognized in stock. The mosaic ateliers of the Vatican contain, it is true, not less than twenty-six thousand different tints; but these, it must be remembered, are simply opaque enamels, while the glass mentioned is all easily translucent, and much of it is clearly transparent.

In the manufacture of this glass the materials employed are much the same as in ordinary sheet and plate glass. It is a double silicate of lime and soda, the coloring being due to the addition of metallic oxides which are soluble in the fused glass. The materials



needed for the basis are, as before, sand, limestone, and alkali. They are mixed in the proper proportions—that is to say, about thirty parts of lime and forty of soda to every hundred parts of sand—and are fused in fire-clay crucibles in the customary glass-furnace. The coloring matter is added at different stages of the process, according to the nature of the material.

The mineral world has been pretty thoroughly ransacked to