Page:Popular Science Monthly Volume 34.djvu/629

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611
GLASS-MAKING.

which, these window-panes are destined to confront. Perhaps the old fable of the wind and the sun comes back to him. The cloak that the one in all its fury could not tear off is gladly thrown aside when the other exerts its power. The same with our pane of glass. It is to repel the rougher storms and winds, yielding passage only to the gentler elements. Sunshine and moonlight are to filter through it, and back of it pleasant fireside pictures are to group themselves. But the imagination is not always so obliging; darker possibilities obtrude themselves as well. The shuddering forms of want and wretchedness are also there, and the solitary dreamer is glad to turn away from them all, and pass out of the open door back again into the world of reality.

PSM V34 D629 Rotary grinding machine for plate glass.jpg

Rotary Grinding Machine for Plate Glass.

The manufacture of crown glass possesses considerable historical interest, but little beyond that. Within the past few years it has been brought into some prominence again from its growing use in decorative windows. It possesses, it is true, a brilliancy much superior to that of sheet glass, but the small size and unequal thickness of the pane obtainable do not permit it to compete successfully with the generous dimensions and remarkable uniformity of the glass now dominant. In mode of fabrication the crown glass proceeds precisely as the sheet up to the time of blowing; at this point the two processes diverge. The ball of semi-plastic glass on the end of the blow-pipe is fashioned into the shape of a cone, as the result of successive rollings on a table of metal or stone, known as the "marver." The process itself goes under the name of "marvering." The apex of the cone forms the so-called "bullion-point." By blowing into the mouth-piece of his pipe, the blower expands the glass into a small globe. This is subsequently enlarged, care being taken that the bullion-point is always kept in line with the pipe. The globe of glass is then