GLASS 



653 



of sand. This mixture is now put into the fire arch, and calcined during the working 

 journey which extends to 10 or 12 hours. Whenever the pots are worked out, that 

 frit is immediately transferred into them in its ignited state, and the founding process 

 proceeds with such despatch that this first charge of materials is completely melted 

 down in 6 hours, so that the pots might admit to be filled up again with the second charge 

 of frit which is founded in 4 hours more. The heat is briskly continued, and in the 

 course of from 12 to 8 hours, according to the size of the pots, the quality of the fuel, 

 and the draught of the furnace, the vitrification is complete. Before blowing the 

 bottles, however, the glass must be left to settle, and to cool down to the blowing con- 

 sistency by shutting the cave doors and feeding holes, so as to exclude the air from the 

 fire-grate and the bottom of the hearth. The glass or metal becomes more dense, and 

 by its subsidence throws up the foreign lighter earthy and saline matters in the form of 

 a scum on the surface, which is removed with skimming irons. The furnace is now 

 charged with coal, to enable it to afford a working heat for 4 or 5 hours, at the end of 

 which time more fuel is cautiously added to preserve adequate heat for finishing the 

 journey. 



It is hardly possible to convey in words alone a correct idea of the manipulations 

 necessary to the formation of a wine-bottle. Six people are employed at this task ; 

 one, called a gatherer, dips the end of an iron tube, about five feet long, previously 

 made red hot, into the pot of melted metal, turns the rod round so as to surround it with 

 glass, lifts it out to cool a little, and then dips and turns it round again ; and so in 

 succession till a ball is formed on its end sufficient to make the required bottle. He 

 then hands it to the blower, who rolls the plastic lump of glass on a smooth stone or 

 cast-iron plate, till he brings it to the very end of the tube ; he next introduces the 

 pear-shaped ball into an open brass or cast-iron mould, shuts this together by pressing 

 a pedal with his foot, and holding his tube vertically, blows through it, so as to ex- 

 pand the cooling glass into the form of the mould. Whenever he takes his foot from 

 the pedal-lever, the mould simultaneously opens out into two halves and falls asunder 

 by its bottom hinge. He then lifts the bottle up at the end of the rod and transfers it 

 to the finisher, who, touching the glass-tube at the end of the pipe with a cold iron, 

 cracks off the bottle smoothly at its mouth-ring. The finished bottles are immediately 

 piled up in the hot annealing arch, where they are afterwards allowed to cool slowly 

 for 24 hours at least. 



2. Broad or spread window-glass. This kind of glass is called inferior window-glass 

 in this country, because coarse in texture, of a wavy wrinkled surface, and very cheap ; 

 but on the Continent spread window-glass, being made with more care, is much 

 better than ours, though still far inferior in transparency and polish to crown-glass, 

 which has, therefore, nearly superseded it use among us. But Messrs. Chance and Co., 

 of Birmingham, make British sheet glass iipon the best principles, and turn out an 

 article quite equal, if not superior, to anything of the kind made either in France or 

 Belgium. Their materials are those used in the crown-glass manufacture. The vitri- 

 fying mixture is fritted for 20 or 30 hours in a reverberatory arch, with considerable 

 stirring and puddling with long-handled shovels and rakes ; and the frit is then trans- 

 ferred by shovels, while red hot, to the melting pots to be founded. When the glass is 

 rightly vitrified, settled, and brought to a working heat, it is lifted out by iron tubes, 

 blown into pears, which, being elongated into cylinders, are cracked up along one side 

 parallel to the axis, by touching them with a cold iron dipped in water, and are then 

 opened out into sheets. The glass cylinders are spread on a bed of smooth stone Paris- 

 plaster, or laid on the bottom of a reverberatory arch ; the cylinder being placed on its 

 gide horizontally, with the cracked line uppermost, gradually opens out, and flattens 

 on the hearth. At one time, thick plates were thus prepared for subsequent polishing 

 into mirrors ; but the glass was never of very good quality ; and this mode of making 

 mirror-plate has accordingly been generally abandoned. 



The spreading furnace or oven is that in which cylinders are expanded into tables 

 or plates. It ought to be maintained at a brisk red heat, to facilitate the softening of 



1087 1088 



the glass. The oven is placed in immediate connection with the annealing arch, so 

 that the tables may be readily and safely transferred from the former to the latter. 



