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Sheet of Glass
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    Owing to the grinding and polishing it is immaterial that the blanks should have a fire-polished surface, but it is still more important that when polished the article should be free from seed, bubbles, striæ and other faults.
    POT PROCESS. Since 1774 when Plate Glass was first made in this country at St. Helens, though not by us, and for some years after the war, the old pot process has carried on with only minor modifications. The frit is filled into the pots through an opening in the furnace door in the manner which has already been described. Each pot contains about a ton of glass and yields a plate of about 300 sq. ft. at a thickness of 7/16". When the melting, founding and fining processes are complete, a pot is removed from the furnace and carried on a bogie to the casting table.
    Here the pot is raised by a "teeming" crane, which turns it over and pours the molten glass on the table in front of the roller in the form of a bolster. The moving roller converts it into a flat sheet, which is then pushed into an annealing kiln, where it used to remain for three days. This annealing kiln was superseded in England in 1902 by a lehr, i.e. a series of kilns into which the plate is pushed, gradually decreasing in temperature, until it is solid enough to travel on rails, by means of which it is carried on a series of movements to the cold end. This reduces the period of annealing for glass ½" thick from three days to 2½ hours.
    BICHEROUX PROCESS. The old pot process is not yet obsolete, but in most countries it has been superseded by a method called the Bicheroux casting process, in which the glass is made in a pot as before, but is poured between two rollers instead of on to a table. The same kind of furnace