Glass Blowing.

North Otago Times, 2 December 1911, Page 3 (Supplement)

Glass Blowing.

Almost all glass (says "CassoH's, Magazine") la blown, and machines have lately been Introduced for blowing glaps bottles by imelimatlc power. Even sheet glass for windows Is first blown, and the large cylinders thus formed are' swung round to elongate them, the hot glass bdng quite tenacious enough to. stand tills treatment; they are then slit down the side with a diamond, and afterwards subjected to such heat In a flattening oven as pauses the cylinder gradually to faTl down as a flat sheet on the floor; the workman then'smooths it out 'with charred wood tad to a handle. Blowlug, however, is not employed In making plate-glass, In this process the white-hot pot la drawn from the furnace by huge forceps on to a ; trolly; then lt-ls wheeled to the casting table,, where a powerful crnno lifts It' up. When tilted, out pours the thick liquid like red-hot treacle on to the table.: Instantly It begins to spread, the Iron Bides to the table preventing. It front pouring over; a roller is passed to and fro over the cooling glass, which Is thus smoothed Into a plate. After being annealed the plate Is ground first by rubbing sand aud water over It, and afterwards coarse emery powder, the result being the smooth and brilliant surface belonging to line plate-glass. The whole process is so delicate, and requires so much care,- that the workmen become usually quite silent while they are busy, forming a striking contrast to the " chairs" of men and boys turning out bottles by the million, at Barron's; Sere tho lads sing and shout'to their hearts' content us they run about with the Iron roils and newly-made bottles. A somewhat similar process 10, that of making plate-glass, though necessarily on a smaller scale, Is that of making glass tiles for rooting; these tiles may also bo seen at lftirron's 6lde by side with the boftlcs, the .glass being poured on a I small curved table, then rolled, and hurried nway.to the annealing oven. ! Thus, then, while the essence of or- : diiuiry glass-milking is by .blowing—or blowing In combination with moulding--1 there Is a special process for plntc-ghisg j awl glass tiles, Another method must Ibe added—that of ■ glass-pressing,"' by I means of which cheap articles, such as small dishes, tumblers,' &c„ are made. In tills process the red-hot Kliisa Is [loured into a. mould, frequently 'with patterns cut in It, nuil a reverse moultf, called a plunger, Is pressed down upon the molten glass, and squeezes It out to shape. But It Is clear that such a process could not be used for narrownecked articles sileli as bottles. The glass marbles, however, for aerated water bottles are moulded. On the other hand, many tine glass articles are blown and shaped without moulding.at all. To make a drinking glass-nn-moulded, the metal Is gathered in' the usual way, rolled on the marver, to malie it round, and then blown, A piece of Iron dipped In water and passed, over the centre of the glass " bubble" will cause it to crack, ai>;l the rod, with half the bubble adhering, being handed to the "gaffer," he rolls it backward and forward on his knees or chair-arms with his left hand, while with his right hand lie moulds it to any shape required by means of simple Instruments, such ! as shaped pieces of wood, which will smooth and equalise the sides.'

It Is, liowever, the "cutting" which causes one remarkable dlffcrciico between simply -moulded or" pressed" glass and the finer forms. The " cutting" of glass la really accomplished by "grinding," . Vessels that are to bo " cut" are Mown with thick walls, and are usually of " flint" glass. The flrst grinding wheel is of Iron, about a foot In diameter, and hung perpendicularly like a lculfe-grhulor's wheel; over It Is suspended a cistern, from which flows on to the wheel a mixture of saml and water; the workman holds the glass object to the revolving wheel, and grinds out roughly the pattern Intended; another wheel Is of stone, and assists In perfecting the pattern, while other wheels are, somo of them, very small, and have a cutting edge. For some patterns small copper wheels, a quarter of an Inch In diameter, are used, and lubricated with oil and emery "powder. The final polishing la sometimes given liy a wooden wheel and moist oxide of tfn—iiopulnrly Known m putty powder. By means of these various wheels a skilful workman-will" cut" any pattern on Hint glass, and the facets so produced will (lash like diamonds In the light. Before cutting, however, the glass is annealed, All glass must bo annealed, or, like some 111-tempered people, It would " fly" at the slightest touch. In annealing the glass, It Is first placed In a low heat, which Is gradually raised to a much higher temperature and then gradually cooled, This process Is sometimes accomplished toy means of gradually cooled. This process Is sometimes accomplished by means of "lears'-that is, long ovens with travelling floors, which carry the glnss slowly through the requisite temperatures. At Barron's the bottles are fed Into travelling furnaces. These are built of brick on iron frames placed on wheels and containing a lire; when tilled, the travelling furnace can bo dragged away on rails from the glass-making furnace toother parts of the extensive yard and left to cool down.