« ZurückWeiter »
bustible body is present, it is usual in some ma. glass is termed blowing, from its being in a nufactures to add a little white oxyd of arsenic. great measure performed by the nperator blowThis supplying oxygen, the combustible is burnt, ing through an iron tube, and by that means inand flies off; while the revived arsenic is at the flating a piece of glass whieh is heated so as to same time volatilized.
become soft and exceedingly pliable. By a series There are several kinds of glass adapted to of the most simple and dexirous operations, this different uses. The best and most beautiful are beautiful material is wrought into the various the flint and the plate-glass, These, when well utensils of elegance and utility, by methods niade, are perfectly transparent and colourless, which require but very few tools, and those of heavy and brilliant. They are composed of fixed the most simple construction. alkali, pure silicious sand, calcined Aints, and The glass-blowers’furnace is of a circular form, litharge, in different proportions. The flint as shewn in the plan, fig. 2, Plate 82. It consists glass contains a large quantity of oxyd of lead, oftbree distinct parts. The lowest is a large arch, which by certain processe's is easily separated. wbich is carried beneath the centre of the furnace: The plate-glass is poured in the melted state upon in the plan, fig. 2, this is represented by the & table covered with copper. The plate is cast dotted lines AA: in the section, fig. 1, nothing of half an inch thick, or more, and is ground down this arch is seen, except part of its upright sides to a proper degree of thioness, and then polished. AA. In the centre of the furnace the covering of
Crown glass, that used for windows, is made this arch is wanting, and its place is supplied by without lead, chiefly of fixed alkali fused with a grate, (represented in the plan) upon which the silicious saod, to which is added some black fire is made. The arch AA, which is called the exyd of manganese, which is apt to give the draught arcb, is intended to bring a constant sup. glass a tinge of purple.
ply of fresh air to the furnace. The second part Bottle-glass is the coarsest and cheapest kind: of the furnace is a circular wall KK, of masonry into this little or no fixed alkali enters the compo- or brick-work, strengthened by pine ribs or piers sition. It consists of an alkaline earth combined BBB, which extend from the foundation to the with alumina and silica. In this country it is top of the furnace, (as shewn in the section), composed of sand and the refuse of the soap. Within the circular wall or waist of the furnace, boiler, which consists of the lime employed in the crucibles or pots to contain the glass are placed; rendering his alkali caustic, and of the earthy these are nine in number, and are situated be. matters with which the alkali was contaminated, hind the spaces between each pier. The fire is The most fusible is flint-glass, and the least made upon the grate in the centre of the furnace, fusible is bottle-glass.
and its flames are reverberated down upon the Flinl-glass melts at the temperature of 109 pots by a dome DD, fig. 1, called the vault, conWedgwood; crown-glass at 30°; and bottle- structed of fire-bricks. The vault, and indeed glass at 47o. The specific gravity varies between the whole superstructure of the furnace, is sup. 8-48 and 3:33.
ported only by the nine piers B : by this means Glass is often tinged of various colours by mixnine apertures are left beneath the vault, which ing with it while in fusion some one or other of are the mouths of the furnace. the metallic oxyds; and on this process, well The vignette at the top of Plate 81, is a view moducted, depends the formation of pastes or of the interior of a glass-house, with workmen factitious gems.
performing the various operations. In this figure, Blue glass is formed by means of oxyd of co. ihe nine mouths of the furnaces are represented balt.
as partially closed by a screen of fire-bricks, in Green, by the oxyd of iron or of copper. which are three apertures to give the workman Violet, by oxyd of manganese.
access to the pots; the use of the screen is to deRed, by a mixture of the oxyds of copper and fend the workman as much as possible from the iron.
heat of the furnace; and the apertures are there. Purple, by the purple oxyd of gold.
fore proportioned to the size of the work to be White, by the oxyd of arsenic and of zinc. performed. The nine pols are placed exactly be.
Yellow, by the oxyd of silver and by combus- neath the mouths of the furnace, and are arranged tible bodies.
round the furnace upon a circular course of brickOpticians, who employ glass for optical in- work (EE in the elevation), so that the current of struments, often complain of the many defects flame reflected from the vault DD, strikes directly under which it labours. The chief of these are upon thein. The flame and heated air are carried ibe following:
off from the surnare by pine fiues, five of which Streaks. These are waved lines, oflen visible FET, are seen in fig. 1, Pl. 82, into an upper in glass, which interrupt distinct vision. They dome GG, which is the third part. It has a cyare probably owing sometimes to want of com- lindric chinwey HH, erected on the top of it, and plete fusion, which prevents the different materials carried up some heighi, to cause sufficient draught from combining sufficiently; but in soine cases for the fire. also they may be produced by the workmen lift. The implements used by a glass-blower are ing up, at two different times, the glass which is neither numerous nor expensive: the principal of to go to the formation of one vessel or instrument. them are hewn in tig 2, PI. 81. A is the blowing
Tears. These are white specks or knots, occa. pipe, an iron tube about three feet six inches siooed by the vitrified clay of the furnaces, or by long, and covered at one end with yarn, to prethe presence of some foreiga salt.
vent it burning the workman's hand. Bis an iron Bubbles.-These are air-bubbles which have rod, of which the workman has several. D are not been allowed to escape. They indicate want the pliers, with which the glass is worked: they of complete fusion, either from too little alkali, are made of stcel, and the circular part being reor the application of too little heat.
duced very thin, acts both as a spring and a joint Cords. These are asperities on the surface of to tbe blades. E are shears used in cutting the the glass, in consequence of too little heat. glass while in a soft and pliable state. Fare ca
GLASS-BLOWING. The art of forming vessels of lipers used for measuring the work occasionally, To give a general idea of the art of forming glass manages the metal, so that it extends two 1 vessels, it will be neeessary to choose some one as three feet in a cylindrical forin. It is then to an example; for this purpose we liave selerted a ried to the fire, and the operation of blowing: decanter, fig. 6. To form this the glass.blower, peated till the metal is stretched to the dime or a boy who assists him, introdures his blowing. sions requirrel, the side to which the pipe is fixed iron A through the side aperture in the mouth of diminishing gradually till it ends in a pyramidal the furnace, and dipping it into the melled glass, for; but, in order to bring both ends nearly to he turns it round at the same time, so as to gather the same diameter, while the glass continues a small quantity of glass at the end of it. Then, flexible, a small portion of hot metal is added to taking it from the furnace, he roils it on the iron the pipe; the whole is drawn out with a pair or plate or niarble dah, as represented on the right iron pincers, and the same end is cut off with a hand side of the vignette; the boy is seen nol far little cold water as before. from him.
The cylinder thus open at one end is returned Wien behos, by repeating this operation two or to the mouth of the furnace, where it is cut by three times, accumulated a sullicienç of metal the aid of cold water, after which it is gradually to form the vessel, he blows through the tube, as leaied on an earthen table, in order to unfold its represented in the centre ofthe vignette. By this length, while the workman with an iron tool almeans the glass is intlated like a bladder, fix. 4: ternately raises and depresses the two halves of and ly rolling it again on the slalı, iris brought the cylinder. to the proper size. The artizan now seats him. Plate-glass is the last and most valuable kind, selfin ile scat represented behind carin wurkman, and is thus called from its being cast in plates or and placing his blowing-pipe across the iwo pieces large sheets: it is almost exclusively einplored of wood, which are exactly similar to the elbows for mirrors or looking glasses, and for the wiu. of an armchair, he rolls the pipe alone the arms dows of carriages. with his left hand, while he lirms the glass ves. Plate-glass was formerly blown; but that mesel, which projects over the arm with the pliers thod having been found very inconvenient, castheld in the right hand. This operation is seen ing was invented ; namely, the liquid metal is at the left hand of the vignette. All the same time conveyed from the furnace to a large table, on that lie holds the vessel in the plier D, as shewn which it is poured, and all excrescences, or bubin fig. 3, he turns it round by roliing the blowing. bles, are immediately removed by a roller that is iron. By this means it is made truly cirrular. swiftly passed over it. It is thien annenled in The end is fattened to make the bottom of the the mauner already referred to. decanter, hy the flat blade of the pliers pressed GLASS ( Painting in). The ancient manner of against it, while it is turning round. It is to be painting in glass was very simple: it consisted in observed, that the pliers or any tools which are to the mere arrangement of pieces of glass of differtouch lle glass, must be rubbed with bees wax, or ent colours in some sort of symmelry, and consti. the cold metal would crack the glass. When these tuted what is now called Mosaic work. (See Moproceedings bare brought the decanter to the SAIC). In process of time ihey came to attempt state of fig. 3, the boy brings the rod B with a more regular designs, and also to represent small portion of glass at the end; sticking it to figures heightened with all their shades: yet they tie bottom of the vessel, the workman touches proceeded no farther than the contours of the the neck with a piece of cold iron, and the glass figures in black with water-colours, and hatching instantly separates from the blowing-pipe. The the dra peries after the same manner on glasses of boy then heats the glass at the furnace mouth; the colour of the ohjeet they designed to paint. and when he returns it the workman opens the For the carnation they used glass of' a bright red south of the decanter with the point of the pliers, colour; and upon this they drew the principal
at fig. 5. The rings on the neck are put on by lineaments of the foce, &c. with black. At the boy bringing a piere of hot glass, a, fig. 6, length, the taste for this sort of painting improve and rolling it round the neck: then cutting it off ing considerably, and the art being tound appli. try the shears E, and smoothing it by the pliers, cable to the adorning of churches, palaces, &c. the decanter is broken off from the rod B, and they found out means of incorporating the cothe operation is completed. Another boy now lours in the glass itself, by heating them in the carries it by putting a long stick into the mouth, fire io a proper degree, having first laid on the and thus conveys it into the top) compartment of colours. A French painter at Marseilles is the furnace over the vault. The manner of doing said to have given the first notion of this im. this is shewn at the left-hand side of the furnace. provement, upon going to Rome under the ponIsere the glass remains several hours at a consi. tificate of Julius II.; but Albert Durer and derable heat, inulitis thoroughly annealed, and Lucas of Leyuen were the first that carried it ioses that brittleness which it would have without to any height. such an operation. A common glass bottle for This art, however, has frequently met with much wine is first brought to the state of K, fig. 7. interruption, and sometimes been almost totally
This is placed in the mould GH, the two halves lost; of which Mr. Walpole gives the following vi' which are shut down together, and the ring l account in his Anecdotes of Painting in England: put over the handles kk to keep it shut. The " The first interruption givev to it was by the reworkman then blows through his tube B, and in formation, which banished the art out of churches; tates the glass so as to fill the mould: by this yet it was in some manner kept up iu the escutmeans al the bottles will be of one size.
cheons of the nobility and gentry in the windows Watch-glasses are made by first blowing a biol- of their seats. Towards the end of queen Elizalow globe, the proper radius for the glasses; beth's reign, indeed, it was omitted even there; then by touching it with the iron ring, fig. 8. yet the practice did not entirely cease. The chapel This cracks out a watch-glass in an instant. of our Lady at Warwick was ornamented anew The same globe will make several glasses. by Robert Dudley earl of Leicester and his count
Window or table-glass is worked nearly in the ess, and the cipher of the glass-painter's name yet manner above described: the workman blows and remains, with the date 1574; and in some of the