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Spinn. Within the past few years, glass-reflectors and the covered (fig. 7). The first is used for meltfor telescopes, of great size and accuracy, have been ing common glass, such as window and bottle glass, made in France. See TELESCOPE.
the other for flint glass. In each case the pots are As regards processes of making, that called the cylindrical was used by the ancients, and is mentioned by Theophilus at the end of the 12th century. The rotatory process was first introduced in Bohemia, subsequently into France in 1730, but not into England till 1832. I'ressed glass was invented in America. In England, the tendency has been to throw the trade into fewer hands, there having been 24 window-glass factories in 1847, and only 8 in 1858; but the value of the export increased from £26,694 in 1818 to about £500,000 in 1855.– Franks,
Fig. 7. A. W., Vitreous Art in the Art Treasures of the United Kinglom (Manchester) Exhibition (4to, 1858); made by hand, and require great skill and care. Pellat, A., Curiosities of Glass-muking (4to, Loucl. The bottom is first moulded on a board. When 1849); Exhibition of Works of Inulustry of all the bottom is finished, the workman begins to Nations (1851); Reports of Juries (1852), Cl xxiv. build up the side of the pot by first forming a
ring of the same height all round, taking care to Manufacture.—The manufacture of glass, as at round off the upper edge to a semicircular curve present carried on, may be classed under the follow- of great regularity; upon this he begins bending ing heauls : Bottle-glass, Crown Window-glass, Sheet over other lumps of the paste until another equal Window-glass, Plate-glass, Flint-glass, Coloured layer is formed, and these are continued until the glass. The first is the coarsest kind in com- pot is complete ; but the workmen do not work
In this country, it is maile generally continuously at each pot until it is finished, they of soap-makers' waste (which contains a quantity leave off from time to time, spreading wet cloths of soula-sults), fresh-water river-sanı, brick-dust, over the edge when they discontinue working. calcineil-lime, and marl ; to these a quantity of This is necessary, to admit of a certain amount of cullet, or the broken glass of the works, is always drying, otherwise the large weight of clay used addel at a certain stage of the manufacture. This would prevent the form from being kept, and the is the mixture employed in making what are called pot would fall to pieces, or lose shape seriously, black butlles, used for wine, beer, &c. Of late the building of the pot is consequently extended years, light-green coloured glass has been preferred over several days. Those made in the form of for many purposes, such as melicine bottles, soila. fig. 6 are from three to four inches thick, but the water bottles, &c. This colour is commonly pro tint-glass pots are only from two to three inches. duced by adding a large proportion of the culet of After the potter has finished his work, the pots are crown glass, which, by its light colour, dilutes the removed into the first drying-tloor, where they are darker material ; if, however, it is wanted of a only protected from draughts, so that the drying liner quality, it is made of sand of a liglit colour, may be conducted with the greatest possible unicontaining only about two-tenths per cent. of the formity. When they have progressed sutficiently, oxide of iron. To 50 parts of this sand are added they are removed to the second drying-tloor, which 20 parts of heavy spar (sulphate of Buryta), 30 parts, is heated with a stove, and the drying is here comif soap-makers' waste, and about two-tenths per pleted. They are then placed in the store, where cent. of oxiile of manganese,
usually a good stock is kept on hand, as time In France, kelp and wooul-ashes are used to fur- improves them, and they are seldom kept less than nish the alkaline portion of the mixture; in other six or nine months. When required for use, they respects, the material is essentially the same. In are placed for four or five days in the annealing Germany, where a rich brown tint is in fashion for turnace, which is on the reverberatory principle, and bottles for the light-coloured Rhine wines, the they are there kept at a red heat. This furuace is materials consist of a light-coloured clay, 10 parts ; so situated, that the pots, when ready, can be most a light yellow-coloured sapıl, 20 parts; kelp, 8 quickly transferred to the main furnace—an operparts; wood-ashes, 38 parts ; cullet, 15 parts; and ation of exceeding difficulty, and requiring great oxide of manganese, 3 parts.
skill and dexterity, as they have to be removed One of the tirst essentials to a successful manu. whilst red-hot, and it must be done so quickly that facture of glass, is the preparation of the melting: no sudden cooling shall injure the pot, a difficulty pots. These pots are composed of clay, which is which can only be understood by remembering that required to be as free as possible from lime and the ordinary pots are nearly four feet in depth, are iron. A clay obtained from the carboniferous shales the same in width at the mouth by about thirty of Worcestershire, in the neighbourhood of Stour- inches at the bottom, and they weigh several hriilge, is the most esteemeil for this purpose ; it hundredweights. The enormous amount of labour consists of pretty nearly equal proportions of silica bestowed upon those pots makes them very expen. and alumina. The clay is carefully «lried and sifted, sive, their value being from £6 to £10 each. Their after which it is mixed with hot water, and worked removal from the annealing oven to the main into a paste ; it is then transferred to the knead. furnace is effected by an immense pair of forceps ing-floor, and when sufficiently kucarled--which is several feet in length, which are placerl horizontaly done by men treating it with naked feet-it is laid upon an upright iron pillar about three feet in in large masses in a damp store-cellar to ripen, a Leight, which rises from a small iron truck on four process the theory of which is not well understood. wheels, so that the whole apparatus can be exsily When required for forming the pots, a sufficient moved from place to place. By means of this quantity is taken and again kneaded with one instrument the pot is listed and dexterously with. frurth of its quantity of the material of olul pots, drawu from the oven, and as quickly transferred to which are ground to tine powder and carefully sifted; its position in the main furnace, in which usually this material gives firmness anıl consistency to the fonr or six are placed on a platform of firebrick or paste, and renders it less liable to be atfected by stone, each pot being opposite to a small arched heat The pots are of two kinds, the open (tig. 6) | opening, through which it cau be tilled aud elu,tiech
The entrance to the main furnace, through which way clear for the blower and moulder, who takes the pots have been introduced, is then closed with his blow-pipe of iron, six feet in length, the part a movable door of firebrick, and covered over with held in the hand being guarded by a covering fireclay to prevent the escape of heat; the pots in of wood and other non-conducting materials. After the furnace are filled with the prepared materials for heating the end of the blow-pipe in the furnace glass, now called fril, mixed with about a sixth or mouth, he dips it into the pot, and turning it eighth part of cullet or broken glass; the openings round, gathers as much metal on the end as is are closed temporarily for two or three hours, by sufficient to form a bottle of the size required which time the tirst charge of material has melted Usually, in bottle making, one gathering suffices, down, leaving room for a further supply, which but in larger operations, such as blowing window. is then thrown into the pot, and this is repeated glass, more gatherings have to be made. Tbe two or three times until the pot is completely operator then blows gently down the pipe, and full. The openings are then closed, and the heat having thus slightly distended the bulb of red increased to the utmost for ten or twelve hours: hot plastic glass (fig. 11, a), he takes it to a plate this part of the operation is called founding, and of polished iron, forming a low bench called the the result of it is to perfectly melt and vitrify the maver, or mavering table. On this he turns it materials. The heat of the furnace is now some round, moulding the round lump of glass into a what reduced, and the scum is removed from the conical form, the change being represented in surface of the melted material, now technically fig. 11, b. This operation, called mavering, is per. called metal, by a workman called the skimmer, formed in all cases where glass is blown; and whose labour requires great care and much expe- as it is necessary that the glass should be pretty rience, as the metal is at a glowing white heat, firm before mavering, it is often cooled by sprink. and is only with difficulty distinguishable in the ling with water, and even, as in the case of fierce white glare of the furnace. The metal is now window-glass and other large blowings, turning ready for the commencement of the journey, as the it in a cavity containing water, which is male operation of working it up is called. This term, by hollowing out a block of wood, usually, if like most others in the glass trade, is derived from attainable, that of the pear-tree, which is said to the French.
be best for the purpose. The arrangements so far apply equally to all After being mavered, the glass is held to the kinds of glass. We now, however, return to the mouth of the furnace, and the operator blows down manufacture of glass bottles, in order the more fully his blow-pipe, and further distends his glass. to understand which, we give the following ground. Formerly, he commenced moulding it into the form plan of one of the houses in which this is carried on of a bottle with his shears, one arm of which was Itig. 8). a is the main furnace, which in this case of charred wood, and the concave bottom was made
by pushing a little piece of glass, called a punty, at the end of an iron rod called the pointel; the blow.
pipe was then detached by a slight blow of the d
shears, and the partly formed bottle was left at the end of the pointel attached by the punty in the hands of a boy who attends upon the man, and brought and applied the punty. The man then
took the pointel in one hand, and after softening
the bottle in the mouth of the furnace, moulded 9
the neck by means of his shears, regulating the
size of the opening by means of a small brass 9
mould, the size and shape of a cork, attachel to b
the midille of the shears; heating the neck again, be formed with a small portion of metal from the pot the ring round the mouth of the bottle. Now, however, after mavering, and the first slight
blowing, the operator inserts the glass into an iron d
or brass moulu, which is formed in two pieces, opening or closing by the pressure of the foot on a lever. When the mould is closed, he blows down
the pipe, and the bottle is completed all bat the f
neck, the ring of which has to be formed by the j
addition of a fresh piece of metal, as before des.
cribed. By this process, bottles are madle with Fig. 8. wonderful vidity and exactness.
At this stage
of the manufacture, by either process, the bottles 18 square, and made to hold only four pots; at each are taken from the workman by a little boy, corner is an opening, which allows the fire to enter who inserts the prongs of a fork into the necks, four small reverberatory furnaces, b, b, b, b, called and carries them to one of the annealing arches arches ; two are called the coarse arches, and the , d, d, d, d, d, where they are carefully arranged others the fine arches. In the two former, the soap. in proper bins until the arch, which usually holds makers' waste is calcined at a red heat for at 144 dozen, is full; it is then closed, and the heat Irast four hours, or whilst a set of pots is being is raised nearly to melting point, and then allowed worked out--that is to say, one journey. Then gradually to subside until it becomes cold, when the calcined material is ground and sifteil in the the bottles are removed to make room for a fresh grinding and sisting house, h, after which it is charge. In the plan, fig. 8, e and f are the sand mingled with the sand, &c., and transferred to the and alkali stores ; 9.9, are stores for the prepared fine arches, where for the term of another journey frit ; and i, j, are sifting-cribs in the sifting-house. it is again calcined. At the end of that time, the Window-glass, whether crown or sheet, is made of pots being empty, are refilled with this material. much more carefully selected materials. They are
When the furnaces are opened for a journey, the slightly varied by different manufacturers, but the skimmer tirst removes the scum, and makes the following are the ingredients used in one of the
largest glass-houses in Great Britain: Sand (well and after turning it about for a minute or two dried), from the neighbourhood of Leighton Buz- in the air until sufficiently cooled, he then dips zard, in Bedfordshire; sulphate of soda, ground; it in again, and over the first he makes a second subcarbonate of soda, white oxide of arsenic, man- gathering, which increases the weight to about ganese, Welsh anthracite, chalk; limestone from three pounds weight; the same cooling , rocess is Hopton Wood, Derbyshire; nitrate of soda; cullet, repeated, and a third gathering is mad., which about as much as is equal to an eighth part of the brings up the weight to about nine pounds; he other ingredients. The exact proportions are only then holds his blow-pipe perpendicularly with the known to the manufacturers. Each ingredient is glass downward, so that it may by its own weight carefully powdered before mixing, and they are pull downward from the pipe in the form of a afterwards calcined or fritted, except the anthra- symmetrical pear-shaped bulb; he next takes it to cite, which is added the pot for the purpose of the hollowed block before mentioned, and turns decomposing the sulphate of soda, and dissipating it round in the water placed in the cavity by its acid; and the manganese and arsenic, which are which it is made ready for the mavering table. only added in very small quantities, to improve the The workman, by skilful management, mavers the colour; too much, however, of each is sure to injure bulb of glass into the form b, fig. 11, and then forms the glass, and therefore these materials can only a little knob at its apex, by turning it on a fixed be safely used by experienced manipulators. The bar of iron called the bullion bar, he then combulk of the glass, however, consists of the sand, and mences blowing, and soon the bulb of nearly solid carbonate and sulphate of soda.
glass is expanded into a large hollow sphere The arrangement of the window-glass houses is (c, fig. 11), still, however, with the little nipple made different, and on a much larger scale than in the by the bullion bar. A little boy now comes forward houses for bottle-glass, and excepting in gathering with an iron rod, the pointel, upon the end of and mavering, all the operations subsequent to the which has been gathered a small lump of metal, founding are differente Fig. 9 will give a general called the punty, about the size of a hen's egg,
this he applies to the nipple, to which it firmly adheres, the workman meanwhile resting his blow. pipe on a fixed rest called the casher-bor, placed for the purpose; by the pressure of the pointil the globe of glass is flattened as in d, fig. 11. The application
of a piece of iron, cooled for the purpose by keeping
it in water, to the junction of the glass with the blow ó'
pipe, detaches it instantly, and the globe of glass is now held with the pointil. The operator carries it
next to the pose-hole (b, fig. 10), and presents the 8
opening formed by the detachment of the blow-pipe,
to the action of the furnace; this again softens the Fig. 9.
glass, which is kept continually revolving by turning
the pointil on an iron rest or hook fixed to the plan of the house for crown window.glass, and fig. 10 masonry of the furnace. The revolucions are at first gives an elevation of one side of the main furnace, slow, but are gradually accelerated as the softening with the three openings through which the glass is of the glass goes on, and the centrifugal force so gathered from the pots. In fig. 9, a is the main produced throws the edges of the orifice outwards, furnace; b, b, two flashing furnaces; the projecting as in e, fig. 11. As the glass flattens, it is revolved piece of brick-work, 1, being the screen which with greater rapidity, and advanced 80 near to the protects the workman from the fire; and c, c are mouth of the nose-hole as to draw the flames outtwo annealing furnaces or ovens.
ward, by contracting the draught. This completes When the founding or melting and the skimming the softening of the glass, which is done suddenly, are completed, the workman takes his blow-pipe, with a rushing noise like the unfurling of a tlag in which is about seven feet in length, heats it at the the wind, caused by the rapid flying outward of the end, and dipping it into the pot of melted glass softened glass and the rush of the flames ontwards.
It becomes perfectly flat, and of equal thickness, except at the bullion or centre, formed, as before described, by the bullion-bar and the punty. The Aashing is pow complete; and the workman removes
it from the nose-hole, and still continuing to turn 6
it in his hands, in order to cool and harden it, as he walks along, carries it to the annealing oven, where another one receives it on a large flattened fork-like implement at the moment the flasher, who has hold
of the pointil, suddenly detaches it by a tonch of his or metal through the opening (a, fig. 10), he gathers, shears. It is then passed through the long horizontal by a slight turn or two, a quantity of glass, about slit which forms the opening into the annealing a pound and a half in weight; this he withdraws, oven, and when fairly in, it is dexterously turned on
Its odge ; here it remains at a temperature somewhat the opening at the blowing end; the heat of the fw below that required to soften glass, until the oven pace soon softens the glass at the closed extremity, is filled with these so-called tables of glass, when of the cylinder, and as the enclosed air is prevented the heat is suffered to decline, until the whole is escaping, as it rarefies, by the thumb placed on cold, when they are removed to the packing-room, the opening of the blow-pipe, it bursts at the softto be packed in crates for sale.
ened part (fig. 13, f.); the operator then quickly Until lateis, crown-glass was almost universally employed for windows, but now that which is called German sheet has become quite as common, besides which British sheet, which is the same glass polished, and plale-glass are much used. The operation of making the sheet-glass is very different from that b.
it quickly so as to draw a line round the cylinder;
after a second or two, he withdraws this line of
The cylinder (fig. 13, 1) is now placed for a short
the bottom, with the diamond-cut upwards. The Fig. 12.
bottom is a perfectly smooth stone, kept constantly
free from dust by the workman; here the heat hea.tel by the Aue B, which opens into the main is sufficient to soften without melting the glass, fum:ace; the lrer, or annealing oven, is often, how and the flatlener, as it softens, opens the two elges over, ar independent structure ; c, C, C, C, C, C, c, c, of the crack until they fall outward flat on the are the eight pots, which is the number usually stone; he then takes an implement in the form employed in these works. These, of course, are of a rake, made by placing a piece of charred opposite to the openings for working them, and in wood transversely at the end of a long handle, and front of each opening is a long opening in the ground, this is gently rubbed over the glass, producing a about eight feet deep and three feet in width; very smooth surface. At the back of the flattend, d, d, d, d, d, d, d. The workman stands on the ing arch is an annealing, oven, communicating edge of this pit, and having made his gathering, as with the arch by a narrow horizontal slit, through in the crown-glass manufacture (a, fig. 13), he next which the sheet of glass is now pushed on to mavers it, without, however, using the bullion-rod a plate of iron, which receives it; and as this (b, fig. 13). He next proceeds to blow his glass, plate is one of a series linked together so as to bolding, it downward whilst doing so, that its weight form an endless band, which can be turned round, may widen and elongate the bulb, and from time the sheets move forward into the annealing oven, lo time dexterously swings it round, which greatly where the workman gently lifts them on edge until increases its length (c, d, fig. 13). As it cools rapidly the oven is filled, when, as in the case of crowd. in this operation, he from time to time places his glass, the heat is allowed to decline until perfectly pipe in the rest which is tixed before the furnace- cool, the sheets are then ready for use. Very much mouth, and gently turning it round, he brings it larger sheets are obtained by this process than Again nearly to the melting-point, then he repeats by the former one, hence it is becoming of great the blowing and swinging, standing over the pit, importance; but it is not easy to obtain workmen to enable him to swing it compietely round as it sufficiently powerful and dexterous to blow and lengthens out. These operations are continued until twirl the largest-sized cylinders ; at present, we the cylinder has reached its maximum size, that is, obtain almost all the operatives so employed froid until it is of equal thickness throughout, and suffi. Belgium. ciently long and broad to admit of sheets of the Glass-shades are made in the same manner as required size being made from it (e, fig. 13). Some- above described ; indeed, they are nothing more times these cylinders are made €2 inches in length, than the rounded ends of the cylinders before being allowing sheets of glass 49 inches in length to be burst. When wanted oval or square, these forms made from them. The next operation is to place the are produced by boxes of wood charred ipsiile, of pipe in the rest, and apply the thumb so as to close the size the shades are required, through which the
cylinder is passed when being blown, until the soft of the best quality, and almost every manufacturer glass touches, and receives shapes from the inside has his own private formula for the inixture. It of the box or mould: they are afterwarıls annealed, may, however, be said to consist chiety of sand and and cut to the lengths required. If of large diame alkaline salts, as in other kinds of girlss, and tho ter, they require immense strength and great skill following is one receipt known to be in use: Fine in the operator, who sometimes aids the power of white sand well washed, to free it from jippurities, his breath by taking into his mouth a little spirit, 720 lbs. ; sulphate of soda, 450 lbs. ; slaked lime, which he blows down the pipe; this, of course, is 80 lbs. ; nitrate of potashı, 25 lbs.; and cullet of plate. instantly converted into vapour, when it reaches glass, 425 lbs. These ingredients, when meltel and the red hot cylinder, and by its expansion aids in skimmed, should yield about 1200 lbs. of perfectly distending the glass.
clear metal, which is the quantity usually required Plute-glaxx is made in a totally different manner; for a casting. When melted and ready for use, the and as its value depends chietly on its purity, the pot is lifted out of the furnace (aa, fig. 14) by meang greatest possible care is taken to procure materials of the forceps, and wheeled up to the casting-tabla
(cc, fig. 14); here it is seized by a crane and tackle, by the narrow openings, ff; and, after they have by which it is lifted, and so nicely poised over sufficiently cooled, are removed through the openthe table, that it can be easily tilted so as to pour ings at each end, g, 9. out its contents. All this requires so much care The plates are next removed to the first polishing. and steadiness, that the men, impressed with the shed, where each is imbedded in a matrix of stucco, great danger of carelessness, usually preserve perfect leaving one surface exposed; the whole is enclosed silence during their work. The table is of large size in a frame, which holds both glass and stucco -20 feet or more in length, by 8 or 10 feet in width. securely. Two of these frames are placed one over When the red-hot liquid glass is poured on, it imme- the other, with the two exposed surfaces of glass ia diately begins to spread; two bars of iron, a little contact. The lower frame is fixed, and the upper thicker than the plate is intended to be, are quickly is made to move by machinery with great rapidity aid on each sidle of the table, and a steel roller is laid backward and forward with a swinging motion, so across, resting on these bars : this roller is worked as to describe an opposite curve with each backward by hand, and rapidly spreads the glass all over the and forward motion. Sand and water are continu. table, the bars preventing it from running over ally thrown on the surface of the fixed plate, and the sides, and regulating its thickness. In a very thus the first stage of polishing is performed. The short time, it begins to cool; the men then seize plates are then readjusted in the frames, and the the end of it with pincers, and pull it forward with other surfaces are brought upwards, and receive a great dexterity on to an endless band of wire-gauze, similar rubbing down with sand and water. The which, being made to revolve, moves the immense plates are next removed to the second polishing. plate forward to a slit-like opening to the annealing room, where women are usually employed; here oven (fig. lt, f), whore it is worked on to another they are again fixed on low tables, and each woman table on wheels, which is pushed forward to make rubs the surface for a long time with a piece of rooin for another. The a. nealing oven is usually of plate-glass, covering from time to time the whole immense length, as, in the case of plate-glass, the face of the plate with emery-powder and water. sheets cannot be set on edgt. At the works at St After both sides have received this hand-polishing, Helen's, in Lancashire, where glass of all kinds is the plates are removed to a third room, where extensively made, there are usually two annealing they are again imbedded on tables which are ovens to each shed, the furnaces being placed movable by machinery, so that the whole surface between them; each oven runs to the end of the of the plate may be brought under the action of shed, and these sheds are usually over 300 feet in the polishers. These are large movable blocks, length. The ground-plan shewn in fig. 14 will give covered with woollen cloth and leather, and loaded • general idea of the arrangement of one of these so as to press on the glass; the polishing material vast work-shops. The main building is a shed, used is colcothar, the red oxide of iron ; this com. with the doors at each end, and both doors and pletes the polish which gives so much beauty to windows are made so as to exclude drafts of air, plate-glass. It is a long and laborious process, and which, if admitted during the operation of cast- is the chief cause of the high price of plate as com. ing, are highly injurions to the quality of the pared with other sheet-glass. British ate is only manufacture. a, a, are the two melting-furnaces ; the cylinder glass polished by the processes just , b, b, b, b, b, the pots ; C, C, the casting-tables ; dee. bed; its comparative cheapness is due to the by d, the endless bands of wire-gauze for moving the rapidity with which the cylinder can be blown. Of plates to the annealing ovens ; e, e, where they enter I thin rapidity, the best estimate may be formed from