FICTILE MANUFACTURES. 



Lambeth in 1673 by Venetian workmen brought 

 over by the Duke of Buckingham. 



A glass-house is usually built in the form of a 

 cone, from 60 to 100 feet high, and from 40 to 80 

 feet in diameter at the base. The furnace is 

 placed in the centre of the building, and is gener- 

 ally of an oblong figure, although sometimes cir- 

 cular. Below the furnace is an arched gallery, 

 extending right across the building, and termin- 

 ating in folding-doors, large enough to admit a 

 barrow for carrying out the ashes, and to afford a 

 sufficient draught of air to the furnace. In the 

 sides of the furnace are apertures called working- 

 holes, through which the blowing-tubes are in- 

 serted. 



Crown-glass. 



Crown or window glass is usually composed of 

 alkali and fine white sand. The best sand for 

 glass-making is that which contains most trans- 

 parent particles, and this is found in large quan- 

 tities in that brought from Lynn-Regis in Norfolk, 

 and the western coast of the Isle of Wight. 



Up to the beginning of the present century, the 

 soda used in making glass was made from kelp, 

 the ashes of burned sea-weed. But in 1792, Le 

 Blanc discovered a method of converting common 

 salt into carbonate of soda ; thus affording to 

 manufacturers a readily obtained and inexhaust- 

 ible supply of alkali. From the introduction of 

 this, a new epoch in the history of glass-making 

 may be dated. The base of all glass is that above 

 stated, but to the alkali and the silica (sand), lime 

 and other ingredients are applied. The lime, in 

 due quantity, promotes the fusion and improves 

 the quality of the mass ; but if too much is 

 present, it renders the glass difficult to work, 

 and subject to devitrifaction. Alumina, which 

 is also sometimes added, and which is always 

 accidentally present, renders the glass liable to 

 devitrifaction. Iron, too, is present in the sand, 

 and as this colours the glass, its effects are got rid 

 of by the addition of manganese. When the soda 

 is introduced in the form of sulphate, or Glauber's 

 Salt, charcoal is introduced, to decompose the 

 salt. Arsenic is also added to decompose other in- 

 gredients. The proportion in which these various 

 materials as sand, soda, charcoal, chalk, mangan- 

 ese, and iron are mixed, varies with circum- 

 stances, and according to the skill of the manu- 

 facturer. To this mixture of materials, a portion 

 of broken waste-glass, termed cutlet, is added, to 

 assist the fusion. 



The pots in which these materials are placed, to 

 be subjected to the action of the furnace, are all 

 made by manual labour, being built up bit by bit, 

 and occupy many months before being ready for 



Fig. ii. 



and thereafter exposed to the action of the kiln. 

 Their shape is that of an ordinary flower-pot with- 

 out a rim (fig. 10). Flint-glass is melted in pots 

 of a different shape, as shewn in fig. 11. They 

 are thus formed to protect the contents from the 

 effects of the flame and smoke, which would bring 

 about a chemical action, tending to reduce the 

 metallic oxides used. The furnace in which the 

 pots are deposited is circular in form, the fire- 

 bars in which the fuel is consumed being in the 

 centre, and nearly on a level with the floor of the 

 glass-house. A series of subterranean passages 

 are placed at various angles with the main or 

 transverse passage, which serves as the ash-pit, a 

 supply of air being thus obtained from different 

 directions. The pots are placed round the cir- 

 cumference, at regular intervals, one on each side 

 of a flue. An aperture is left in the brickwork, in 

 the space between two flues, through which the 

 materials are passed to the pots. The heat is 

 regulated to any degree of intensity, by opening 

 or shutting apertures admitting more or less air 

 to the grate bars. 



The materials are introduced into the pots by 

 means of an iron shovel, the pots being previously 

 brought to a white heat. The aperture is then 

 closed with a stopper, and carefully luted with 

 clay. After subjection for some time to a high 

 temperature, the whole -become thoroughly fused, 

 and enter into chemical combination ; the silica 

 uniting with the bases, soda, lime, &c. (see CHEM- 

 ISTRY) to form silicates. On the mass subsiding, 

 fresh materials are added till the pot is filled with 

 the molten glass, technically called metal. 



The pots last for periods of greater or less ex- 

 tent some for two, three, and even twelve months, 

 while some give way during the preliminary test- 

 ing to which all are subjected. 



The pots being now full of melted glass, the 

 material is ready for the operations of the work- 

 men. An iron tube, six or seven feet in length, 

 thicker at one end than the other, is heated and 

 dipped into the liquid ' metal,' through the work- 

 ing-hole, as shewn in fig. 12. A portion of glass 

 adheres to the thick end of the tube, which, being 



Fig. 12. 



allowed to cool a little, is again dipped in, and 

 gathers more. The rod is then taken out, and 

 lung perpendicularly, that the metal may be 

 equally distributed on all sides, and also that it 

 may be lengthened out beyond the rod. The metal 

 s next rolled upon a smooth iron plate, called the 



use. They are made of the best Stourbridge 



clay, moistened and mixed with about one-fifth of i marver, and afterwards blown out slightly, so as 



ground potsherds, are carefully dried for months, | to resemble a pear in shape. The blower then 



3ul 



