GLASS
Bent Glass.
The number of molds required in a glass-bending establishment is large.
The bending is done in a kiln. Glass melts at 2,300° F.; the heat employed in bending is 1,800° F. No pyrometer would stand long in that heat, so the heat of the kiln is judged from the color of the flame and other indications. Smaller pieces of glass are put into the molds in the kilns with forks made for the purpose. The great molds used for bending large sheets of glass are mounted on cars, that may be rolled in and out of kilns. The glass is laid upon the top of the mold or cavity, and is bent by its own weight. As it is softened by the heat it sinks into the mold and so is bent. It may take an hour or two to bend the glass, which is then left in the kiln from 24 to 36 hours to anneal and cool. Glass of any kind or size is put into the kilns in its finished state; the great heat to which it is subjected does not disturb the polished surface. Despite every precaution more or less glass is broken in bending. Bent glass costs about 50 per cent more than the flat.
The use of bent glass is increasing, and there are 4 or 5 glass-bending establishments in the United States, of which one is in the East.
Colored Glass.
Sand, 65 parts; potash, 15 parts; soda, 5 parts; lime, 9 parts; molybdenite, 3 parts; sulphide of sodium, 2 parts, gave a dark reddish-brown glass. In thinner layers this glass appeared light brownish yellow. Flashed with opal, it became a smutty black brown.
Sand, 50 parts; potash, 15 parts; soda, 5 parts; lime, 9 parts; molybdenite, 1 part; sulphide of sodium, 2 parts, gave a yellow glass.
Sand, 10 parts; potash, 3.3 parts; soda, 0.27 parts; lime, 1.64 parts; molybdenite, 0.03 parts, gave a reddish-yellow glass with a fine tinge of red.
Sand, 100 parts; potash, 26 parts; soda, 108 parts; lime, 12 parts; sulphide of copper, 1.7 parts; sulphide of sodium, 2.3 parts, gave a dark-brown color, varying from sepia to sienna. In thick layers it was no longer transparent, but still clear and unclouded. When heated this glass became smutty black brown and clouded.