Page:The American Cyclopædia (1879) Volume VIII.djvu/23

 GLASS 15 article upon its end when freed from the pipe, adhesion being secured by the softness of the glass or by a little red-hot lump already attach- ed to the punty. Spring tongs, like sugar tongs, are used to take up bits of melted glass ; and a heavier pair, called pucellas, furnished with FIG. 9. Tools used in Glassmaking. 1. Pipe or blowing tube. 2. Pucellas. 8. Shears. 4. Pucel- las with wooden blades. 5. Spring tongs. 6. Battledore. broa'd but blunt blades, serve to give shape to the articles as the instrument in the right hand of the workman is pressed upon their surface, while, seated upon his bench, he causes with his left hand the rod holding the article to roll up and down the two long iron arms of his seat, upon which it is laid horizontally before him. At the same time the vessel is also shaped from the interior as well, and is occasionally applied to the opening of the furnace to soften it entirely or only in some part to which great- er distention is given by blowing. The pu- cellas are sometimes provided with blades of wood, as at 4, fig. 9. Another important in- strument is a pair of shears, with which a skil- ful workman will cut off with one clip the top of a wine glass, as he twirls it round with the FIG. 10 Glass Maker's Chair. rod to which it is attached held in the left hand. The edge softened in the fire is then smoothed and polished. Besides these a wood- en utensil called a battledore is employed, with which the glass is flattened by beating when necessary; compasses and calipers and a 362 VOL. viii. 2 measure stick are at hand for measuring ; and a slender rod of iron forked at one end is used to take up the articles, and carry them when shaped to the annealing oven, in which they are left for some time to be tempered. (See ANNEALING.) The marver (Fr. marbre, marble) is a smooth polished cast-iron slab, upon the surface of which the workman rolls the glass at the end of his tube in order to give it a perfectly circular form. Those used in the manufacture of common black bottles are fur- nished on one edge with several concavities, in which the mass of metal taken from the melt- ing pot is first roughly shaped as it is rolled over and over and made to swell by gentle blow- ing. One of the most ordinary forms into which glass is manufactured is that of bottles, which are made in moulds by the process of blowing, the kind of glass generally used being the or- dinary green or window glass, and flint glass. The method of making bottles is described and illustrated in the article BOTTLE. Bottles for champagne and aerated waters are made of ex- traordinary strength, and are sometimes tested by the pressure of water before being used. Of the various kinds of glass in common use, none require more care to insure the purity of the materials employed than the crystal or flint j glass, of which are made many choice articles ' for domestic purposes, some of which are sub- jected to the processes of cutting or grinding and polishing. It possesses the properties of great transparency and high refractive power, which fit it for lenses for ^optical instruments. Flints calcined and ground were formerly used to furnish the silica, but pure sand is now gen- erally used in its stead. Oxide of lead enters largely into its composition, and to this are due its brilliancy, density, and comparative softness. The oxide should be especially prepared to in- sure its purity. Oxide of zinc has been found to produce similar effects. The fusion must be rapid and at intense heat, and this must be re- duced as soon as the metal is thoroughly melt- ed and refined by the escape of the bubbles of gas, or the product acts upon the alumina and iron of the pot, and is thus so contaminated as to be worthless. The furnace is usually circu- lar in form, and contains from four to ten pots, in front of each of which there is an opening for the workman. In the manufacture of arti- cles of domestic use made of flint glass two processes are in use, blowing and pressing, the latter being very common in the United States. By the former method a mould is sometimes used, as in the case of bottles, when the opera- tions are similar to those described in working ordinary green glass ; or the article may receive its symmetrical form from the skill of the work- man unaided by any mould. This process may be illustrated by describing how a wine glas? in three parts is made. The workman, having gathered on the end of a blowpipe the requisite amount of glass (1, fig. 11), rolls it on the marver and expands it by blowing into the tube until it assumes the form shown at 2, and after-