GLASS.

such in the Revelations and in the Recognitions to England, and transported to Africa and Asia of St Clement, in which St Peter is described in the way of trade. The Venetian glass engaged as praying to see some marvellous columns of this material in the island of Aradus. At the close of the Roman Empire, only two kinds of glass appear to have been manufactured-bottles of a greenish glass in the west, and the hyalina diachrysa, or gilded glass of many colours, in the east. After that period, a few glass vessels have been found in the Anglo-Saxon graves of England, and Frankish sepulchres of France, of a peculiar fabric of green glass with projecting knobs, bent round to the body of the glass, and apparently a rude imitation of the diatreta. The Romans knew the use of soda and lead as fluxes for glass, and made both crown and flint glass. They made most of the fancy varieties at present in use, and were acquainted with the art of colouring it blue by cobalt, green by copper, rose or ruby by gold. Many of their imitations of gems and other fanciful colours were also of Schmeltz glass. But the great site of the glass manufactories of the dark and middle ages was Venice, whither it was transplanted on the foundation of that city in the 7th c. A.D. The art, however, seems to have improved on the conquest of Constantinople by the French in 1204, and in 1291 the establishments were removed to the island of Murano, the manufacturers forming a guild with a libro d'oro, or register of nobility, and the secret kept with the greatest jealousy. In 1436, their colour-glass came into note, and continued so till the close of the century; and in the 16th c., lacepatterns and mirrors were introduced. In the 15th and 16th centuries, plain glass with nice ornaments gilt and enamelled; in the 16th, crackled lace and reticulated glass, vitrodi trino; and in the 17th c., variegated or marbled glasses were

Fig. 4.-German Fig. 5.-Venetian Glass on
Drinking-glass.
open-work stem.

produced. The millefiori glass extends through all periods, and seems to have been derived from the Roman, being continued to the present day, when large quantities of this glass are annually imported

for a long time the monopoly of commerce, their mirrors, goblets, and cups being exported all over the world, but it has been superseded by manufac tures of England and Germany. The forms of the Venetian glass reflected its oriental origin, and the earlier glass of other countries of Europe in their turn shew the derivation of their art from Venice. In Germany, the oldest glass (which was flint) dates from the 16th c., and consists of goblets and tankards of white colour, enamelled with coloured coats of arms and other devices, millefiori, and schmeltz glass. Engraved glass was first introduced by Caspar Lehmann at Prague in 1609 under imperial protection, and continued by his pupil G. Schwanhard; and ruby glass by Kunckel in 1679. Glass is said to have been made in 1294 at Quinquengrone, in Normandy, before the 16th c., in the reign of Philip VI.; and John and the Dukes of Lorraine established manufactories in their domains, and a common kind was made in Dauphiny and Provence. Cast plate is also said to have been established at Cherbourg by artists from Venice, and in 1688 the art was declared noble. Potash, lime, silica, and no lead was employed. Thevart introduced glass casting and plate-glass works at Paris. In France, oxide of lead flint-glass was made at St Cloud in 1784; another manufactory was subsequently established at St Louis in 1790; and the St Cloud establishment was removed to the vicinity of the Mont Cenis, where it flourished till 1827. It is uncertain whether glass was made in England before the 16th c., as that mentioned may have been imported from Flanders or Venice. Window-glass is mentioned by Bede in 674, but was not in general use for windows till the 15th century. In 1557 flint-glass was manufactured at the Savoy and Crutched Friars; in 1565, there were glass-works under Cornelius de Launoy; and in 1567, Jean Quarre and other Flemish manufacturers established works at Crutched Friars, which Quarre's descendants extended to Sussex. In 1615, Sir R. Maunsell obtained a patent for making glass, in consideration of using pit coal instead of wood, and oxide of lead was then introduced in 1635; and in 1673, Venetian artists, brought over by the Duke of Buckingham, manufactured mirrors of plate-glass at Lambeth, and drinking-glasses were made at this period. But Venetian glass was extensively imported. In 1771, the company of British Plate-glass Manufacturers was established at Ravenhead, near Prescot, Lancashire; and in 1728, plate-glass was made by the Cooksons at South Shields, and the Thames Plate-glass Company in 1835-1836. Patent plate was first made in 1840. In Scotland, the manufacture was introduced in the reign of James VI., and George Hay obtained a patent for 31 years. The first glass was manufactured at Wemyss, in Fifeshire, afterwards at Prestonpans and Leith. In 1661, only the prin cipal chambers of the king's palace had glass. In America, attempts seem to have been made to establish glass-works in 1746 at Jamestown, Virginia; subsequently, in 1780, at Temple, New Hampshire; in 1789, at Newhaven; and in 1809, at Boston. Plate-glass was first made there in 1853. It is made at Boston, Baltimore, and New York.

At an early period the application of glass for magnifying lenses appears to have been known. Ptolemy II. had a telescope mounted at the Pharos, and globes filled with water were in use for the purpose of magnifying under the Romans. Lenses are mentioned in the 12th c. A. D. by Alhazan, and by Roger Bacon in the 13th c.; towards the close of which, Salvino d'Armato invented eye-glasses, which were subsequently improved by Alessandro

GLASS.

Spina. Within the present year (1862), glass-reflectors for telescopes, of great size and accuracy, have been made in France. See TELESCOPE.

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. Pressed 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 1848 to about £500,000 in 1855.—Franks, A. W., Vitreous Art in the Art Treasures of the United Kingdom (Manchester) Exhibition (4to, 1858); Pellat, A., Curiosities of Glass-making (4to, Lond. 1849); Exhibition of Works of Industry of all Nations (1851); Reports of Juries (1852), Ch. xxiv. p. 521.

made by hand, and require great skill and care. The bottom is first moulded on a board. When the bottom is finished, the workman begins to 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 heads: 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 mon use. In this country, it is made generally continuously at each pot until it is finished, they of soap-makers' waste (which contains a quantity of soda-salts), fresh-water river-sand, brick-dust, calcined-lime, and marl; to these a quantity of cullet, or the broken glass of the works, is always added at a certain stage of the manufacture. This is the mixture employed in making what are called black bottles, used for wine, beer, &c. Of late years, light-green coloured glass has been preferred for many purposes, such as medicine bottles, sodawater bottles, &c. This colour is commonly produced by adding a large proportion of the cullet of crown-glass, which, by its light colour, dilutes the darker material; if, however, it is wanted of a finer quality, it is made of sand of a light colour, containing only about two-tenths per cent. of the oxide of iron. To 50 parts of this sand are added 20 parts of heavy spar (Sulphate of Baryta), 30 parts of soap-makers' waste, and about two-tenths per cent. of oxide of manganese.

In France, kelp and wood-ashes are used to furnish the alkaline portion of the mixture; in other respects, the material is essentially the same. In Germany, where a rich brown tint is in fashion for bottles for the light-coloured Rhine wines, the materials consist of a light-coloured clay, 16 parts; a light yellow-coloured sand, 20 parts; kelp, 8 parts; wood-ashes, 38 parts; cullet, 15 parts; and oxide of manganese, 3 parts.

One of the first essentials to a successful manufacture of glass, is the preparation of the meltingpots. These pots are composed of clay, which is required to be as free as possible from lime and iron. A clay obtained from the carboniferous shales of Worcestershire, in the neighbourhood of Stourbridge, is the most esteemed for this purpose; it consists of pretty nearly equal proportions of silica and alumina. The clay is carefully dried and sifted, after which it is mixed with hot water, and worked into a paste; it is then transferred to the kneading-floor, and when sufficiently kneaded-which is done by men treading it with naked feet-it is laid in large masses in a damp store-cellar to ripen, a process the theory of which is not well understood. When required for forming the pots, a sufficient quantity is taken and again kneaded with onefourth of its quantity of the material of old pots, which are ground to fine powder and carefully sifted; this material gives firmness and consistency to the paste, and renders it less liable to be affected by heat. The pots are of two kinds, the open (fig. 6)

leave off from time to time, spreading wet cloths over the edge when they discontinue working. This is necessary, to admit of a certain amount of drying, otherwise the large weight of clay used would prevent the form from being kept, and the pot would fall to pieces, or lose shape seriously, the building of the pot is consequently extended over several days. Those made in the form of fig. 6 are from three to four inches thick, but the flint-glass pots are only from two to three inches. After the potter has finished his work, the pots are removed into the first drying-floor, where they are only protected from draughts, so that the drying may be conducted with the greatest possible uniformity. When they have progressed sufficiently, they are removed to the second drying-floor, which is heated with a stove, and the drying is here completed. They are then placed in the store, where usually a good stock is kept on hand, as time improves them, and they are seldom kept less than six or nine months. When required for use, they are placed for four or five days in the annealing furnace, which is on the reverberatory principle, and they are there kept at a red heat. This furnace is so situated, that the pots, when ready, can be most quickly transferred to the main furnace-an operation of exceeding difficulty, and requiring great skill and dexterity, as they have to be removed whilst red-hot, and it must be done so quickly that no sudden cooling shall injure the pot, a difficulty which can only be understood by remembering that the ordinary pots are nearly four feet in depth, are the same in width at the mouth by about thirty inches at the bottom, and they weigh several hundredweights. The enormous amount of labour bestowed upon these pots makes them very expensive, their value being from £6 to £10 each. Their removal from the annealing oven to the main furnace is effected by an immense pair of forceps several feet in length, which are placed horizontally upon an upright iron pillar about three feet in height, which rises from a small iron truck on four wheels, so that the whole apparatus can be easily moved from place to place. By means of this instrument the pot is lifted and dexterously withdrawn from the oven, and as quickly transferred to its position in the main furnace, in which usually four or six are placed on a platform of firebrick or stone, each pot being opposite to a small arched opening, through which it can be filled and emptied.

GLASS.

The entrance to the main furnace, through which the pots have been introduced, is then closed with a movable door of firebrick, and covered over with fireclay, to prevent the escape of heat; the pots in the furnace are filled with the prepared materials for glass, now called frit, mixed with about a sixth or eighth part of cullet or broken glass; the openings are closed temporarily for two or three hours, by which time the first charge of material has melted down, leaving room for a further supply, which is then thrown into the pot, and this is repeated two or three times until the pot is completely full. The openings are then closed, and the heat increased to the utmost for ten or twelve hours: this part of the operation is called founding, and the result of it is to perfectly melt and vitrify the materials. The heat of the furnace is now somewhat reduced, and the scum is removed from the surface of the melted material, now technically called metal, by a workman called the skimmer, whose labour requires great care and much experience, as the metal is at a glowing white heat, and is only with difficulty distinguishable in the fierce white glare of the furnace. The metal is now ready for the commencement of the journey, as the operation of working it up is called. This term, like most others in the glass trade, is derived from the French.

The arrangements so far apply equally to all kinds of glass. We now, however, return to the manufacture of glass bottles, in order the more fully to understand which, we give the following groundplan of one of the houses in which this is carried on (fig. 8). a is the main furnace, which in this case

9

d

d

d.

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d

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way clear for the blower and moulder, who takes his blow-pipe of iron, six feet in length, the part held in the hand being guarded by a covering of wood and other non-conducting materials. After heating the end of the blow-pipe in the furnace mouth, he dips it into the pot, and turning it round, gathers as much metal on the end as is sufficient to form a bottle of the size required. Usually, in bottle making, one gathering suffices, but in larger operations, such as blowing window. glass, more gatherings have to be made. operator then blows gently down the pipe, and having thus slightly distended the bulb of red hot plastic glass (fig. 11, a), he takes it to a plate of polished iron, forming a low bench called the maver, or mavering table. On this he turns it round, moulding the round lump of glass into a conical form, the change being represented in fig. 11, b. This operation, called mavering, is performed in all cases where glass is blown; and as it is necessary that the glass should be pretty firm before mavering, it is often cooled by sprinkling with water, and even, as in the case of window-glass and other large blowings, turning it in a cavity containing water, which is made by hollowing out a block of wood, usually, if attainable, that of the pear-tree, which is said to be best for the purpose.

After being mavered, the glass is held to the mouth of the furnace, and the operator blows down his blow-pipe, and further distends his glass. Formerly, he commenced moulding it into the form of a bottle with his shears, one arm of which was 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 blowpipe was then detached by a slight blow of the 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 the neck by means of his shears, regulating the size of the opening by means of a small brass mould, the size and shape of a cork, attached to the middle of the shears; heating the neck again, he 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 or brass mould, 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 but the neck, the ring of which has to be formed by the addition of a fresh piece of metal, as before described. By this process, bottles are made with wonderful rapidity and exactness. At this stage of the manufacture, by either process, the bottles is 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, 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 least 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 the calcined material is ground and sifted in the grinding and sifting house, h, after which it is mingled with the sand, &c., and transferred to the fine arches, where for the term of another journey it is again calcined. At the end of that time, the pots being empty, are refilled with this material.

f

Fig. 8.

h

d

When the furnaces are opened for a journey, the skimmer first removes the scum, and makes the

gradually to subside until it becomes cold, when the bottles are removed to make room for a fresh charge. In the plan, fig. 8, e and ƒ are the sand and alkali stores; g, 9, are stores for the prepared frit; and i, j, are sifting-cribs in the sifting-house.

Window-glass, whether crown or sheet, is made of much more carefully selected materials. They are slightly varied by different manufacturers, but the following are the ingredients used in one of the

GLASS.

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 Hopton Wood, Derbyshire; nitrate of soda; cullet, about as much as is equal to an eighth part of the other ingredients. The exact proportions are only known to the manufacturers. Each ingredient is carefully powdered before mixing, and they are afterwards calcined or fritted, except the anthracite, which is added in the pot for the purpose of decomposing the sulphate of soda, and dissipating its acid; and the manganese and arsenic, which are only added in very small quantities, to improve the colour; too much, however, of each is sure to injure the glass, and therefore these materials can only be safely used by experienced manipulators. The bulk of the glass, however, consists of the sand, and carbonate and sulphate of soda.

The arrangement of the window-glass houses is different, and on a much larger scale than in the houses for bottle-glass, and excepting in gathering and mavering, all the operations subsequent to the founding are different. * Fig. 9 will give a general

three pounds weight; the same cooling process is repeated, and a third gathering is made, which brings up the weight to about nine pounds; he then holds his blow-pipe perpendicularly with the glass downward, so that it may by its own weight pull downward from the pipe in the form of a symmetrical pear-shaped bulb; he next takes it to the hollowed block before mentioned, and turns it round in the water placed in the cavity by which it is made ready for the mavering table. The workman, by skilful management, mavers the bulb of glass into the form b, fig. 11, and then forms a little knob at its apex, by turning it on a fixed bar of iron called the bullion bar; he then commences blowing, and soon the bulb of nearly solid glass is expanded into a large hollow sphere (c, fig. 11), still, however, with the little nipple made by the bullion bar. A little boy now comes forward with an iron rod, the pointel, upon the end of which has been gathered a small lump of metal, 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 blowpipe on a fixed rest called the casher-box, placed for the purpose; by the pressure of the pointil the globe of glass is flattened as in d, fig. 11. The application

plan of the house for crown window-glass, and fig. 10 gives an elevation of one side of the main furnace, with the three openings through which the glass is gathered from the pots. In fig. 9, a is the main furnace; b, b, two flashing furnaces; the projecting piece of brick-work, b', being the screen which protects the workman from the fire; and c, c are two annealing furnaces or ovens.

When the founding or melting and the skimming are completed, the workman takes his blow-pipe, which is about seven feet in length, heats it at the end, and dipping it into the pot of melted glass

Fig. 11.

of a piece of iron, cooled for the purpose by keeping it in water, to the junction of the glass with the blowpipe, detaches it instantly, and the globe of glass is now held with the pointil. The operator carries it next to the nose-hole (b, fig. 10), and presents the opening formed by the detachment of the blow-pipe, to the action of the furnace; this again softens the glass, which is kept continually revolving by turning the pointil on an iron rest or hook fixed to the masonry of the furnace. The revolutions are at first slow, but are gradually accelerated as the softening of the glass goes on, and the centrifugal force so produced throws the edges of the orifice outwards, as in e, fig. 11. As the glass flattens, it is revolved with greater rapidity, and advanced so near to the mouth of the nose-hole as to draw the flames outward, by contracting the draught. This completes the softening of the glass, which is done suddenly, with a rushing noise like the unfurling of a flag in the wind, caused by the rapid flying outward of the softened glass and the rush of the flames outwards. 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 flashing is now complete; and the workman removes it from the nose-hole, and still continuing to turn 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 touch of his shears. It is then passed through the long horizontal slit which forms the opening into the annealing oven, and when fairly in, it is dexterously turned on

GLASS.