Page:Popular Science Monthly Volume 37.djvu/175

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GLASS-MAKING.

cles, and similarly with the secondary part of the decoration. This completes the rough work.

The second process is that of "smoothing" and is carried out by means of wheels made of a natural stone found in Scotland, known as the Craig Leigh stone. A large part of modern Edinburgh is built out of this material. It is a compact silicious stone, wearing very uniformly, and almost free from that tendency to crumble which characterizes the majority of our native sandstones. The stone wheels are about the same size as the iron wheels used in the roughing process; but their cutting edges, instead of being smooth, are beveled, thus giving a sharp edge in the center of the face. PSM V37 D175 Sand blasting glass.jpgFig. 4.—The Sand-Blast in Operation. This is occasionally sharpened by regrinding, or by holding pieces of flint against the beveled faces of the revolving wheel. A tiny stream of water falls constantly against the face of the stone. Each cut made on the iron wheel is gone over on the stone, and, by the finer friction, the surface of the facets becomes smooth and transparent. The carafe is slowly becoming an object of beauty.

Next in the order of the processes comes the polishing, which is effected by wooden wheels mounted as before and supplied with pumice or rotten-stone. Red willow is considered the best material for the polishing-wheel, though poplar is also frequently used. The hard woods are found to be less suitable for the purpose. The wooding—for so this third process is called in the atelier—gives a fine finish to the smoothed facets and adds greatly to their brilliancy. It is a process, however, which is only practicable in cases where the cutting is rather deep. Where it amounts to little more than a tracing, the wooden wheel would be of slight use.

Still a fourth process is required before the carafe is ready to