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bustible body is present, it is usual in some manufactures to add a little white oxyd of arsenic. This supplying oxygen, the combustible is burnt, and flies off; while the revived arsenic is at the same time volatilized.
There are several kinds of glass adapted to different uses. The best and most beautiful are the flint and the plate-glass. These, when well made, are perfectly transparent and colourless, heavy and brilliant. They are composed of fixed alkali, pure silicious sand, calcined flints, and litharge, in different proportions. The flint glass contains a large quantity of oxyd of lead, which by certain processes is easily separated. The plate-glass is poured in the melted state upon a table covered with copper. The plate is cast half an inch thick, or more, and is ground down to a proper degree of thinness, and then polished. Crown glass, that used for windows, is made without lead, chiefly of fixed alkali fused with silicious sand, to which is added some black oxyd of manganese, which is apt to give the glass a tinge of purple.
Bottle-glass is the coarsest and cheapest kind: into this little or no fixed alkali enters the composition. It consists of an alkaline earth combined with alumina and silica. In this country it is composed of sand and the refuse of the soapboiler, which consists of the lime employed in rendering his alkali caustic, and of the earthy matters with which the alkali was contaminated. The most fusible is flint-glass, and the least fusible is bottle-glass.
Flint-glass melts at the temperature of 10° Wedgwood; crown-glass at 30°; and bottleglass at 47°. The specific gravity varies between
2-48 and 3-33.
Glass is often tinged of various colours by mixing with it while in fusion some one or other of the metallic oxyds; and on this process, well conducted, depends the formation of pastes or factitious gems.
Blue glass is formed by means of oxyd of cobalt.
Green, by the oxyd of iron or of copper.
Red, by a mixture of the oxyds of copper and iron.
Purple, by the purple oxyd of gold. White, by the oxyd of arsenic and of zinc. Yellow, by the oxyd of silver and by combustible bodies.
Opticians, who employ glass for optical instruments, often complain of the many defects under which it labours. The chief of these are the following: Streaks.-These are waved lines, often visible in glass, which interrupt distinct vision. They are probably owing sometimes to want of complete fusion, which prevents the different materials from combining sufficiently; but in some cases also they may be produced by the workmen lifting up, at two different times, the glass which is to go to the formation of one vessel or instrument. Tears.-These are white specks or knots, occasioned by the vitrified clay of the furnaces, or by the presence of some foreign salt.
Bubbles. These are air-bubbles which have not been allowed to escape. They indicate want of complete fusion, either from too little alkali, er the application of too little heat.
Cords. These are asperities on the surface of the glass, in consequence of too little heat. GLASS-BLOWING. The art of forming vessels of
glass is termed blowing, from its being in a great measure performed by the operator blowing through an iron tube, and by that means inflating a piece of glass which is heated so as to become soft and exceedingly pliable. By a series of the most simple and dextrous operations, this beautiful material is wrought into the various utensils of elegance and utility, by methods which require but very few tools, and those of the most simple construction.
The glass-blowers' furnace is of a circular form, as shewn in the plan. fig. 2, Plate 82. It consists of three distinct parts. The lowest is a large arch, which is carried beneath the centre of the furnace: in the plan, fig. 2, this is represented by the dotted lines AA: in the section, fig. 1, nothing of this arch is seen, except part of its upright sides AA. In the centre of the furnace the covering of this arch is wanting, and its place is supplied by a grate, (represented in the plan) upon which the fire is made. The arch AA, which is called the draught arch, is intended to bring a constant supply of fresh air to the furnace. The second part of the furnace is a circular wall KK, of masonry or brick-work, strengthened by nine ribs or piers BBB, which extend from the foundation to the top of the furnace, (as shéwn in the section). Within the circular wall or waist of the furnace, the crucibles or pots to contain the glass are placed; these are nine in number, and are situated behind the spaces between each pier. The fire is made upon the grate in the centre of the furnace, and its flames are reverberated down upon the pots by a dome DD, fig. 1, called the vault, constructed of fire-bricks. The vault, and indeed the whole superstructure of the furnace, is supported only by the nine piers B: by this means nine apertures are left beneath the vault, which are the mouths of the furnace.
The vignette at the top of Plate 81, is a view of the interior of a glass-house, with workmen performing the various operations. In this figure, the nine mouths of the furnaces are represented as partially closed by a screen of fire-bricks, in which are three apertures to give the workman access to the pots; the use of the screen is to defend the workman as much as possible from the heat of the furnace; and the apertures are there. fore proportioned to the size of the work to be performed. The nine pots are placed exactly beneath the mouths of the furnace, and are arranged round the furnace upon a circular course of brickwork (EE in the elevation), so that the current of flame reflected from the vault DD, strikes directly upon them. The flame and heated air are carried off from the furnace by nine flues, five of which FFF, are seen in fig. 1, Pl. 82, into an upper dome GG, which is the third part. It has a cylindric chimney HH, erected on the top of it, and carried up some height, to cause sufficient draught for the fire.
The implements used by a glass-blower are neither numerous nor expensive: the principal of them are shewn in fig. 2, Pl. 81. A is the blowing pipe, an iron tube about three feet six inches long, and covered at one end with yarn, to prevent it burning the workman's hand. Bis an iron rod, of which the workman has several. Dare the pliers, with which the glass is worked: they are made of steel, and the circular part being reduced very thin, acts both as a spring and a joint to the blades. E are shears used in cutting the glass while in a soft and pliable state. Fare calipers used for measuring the work occasionally,
To give a general idea of the art of forming glass vessels, it will be necessary to choose some one as an example; for this purpose we have selected a decanter, fig. 6. To form this the glass-blower, or a boy who assists him, introduces his blowingiron A through the side aperture in the mouth of the furnace, and dipping it into the melted glass, he turns it round at the same time, so as to gather a small quantity of glass at the end of it. Then, taking it from the furnace, he roils it on the iron plate or marble dab, as represented on the right hand side of the vignette; the boy is seen not far from him.
When he has, by repeating this operation two or three times, accumulated a sufliciency of metal to form the vessel, he blows through the tube, as represented in the centre of the vignette. By this means the glass is inflated like a bladder, fig. 4: and by rolling it again on the slab, it is brought to the proper size. The artizan now seats him selfin the seat represented behind each workman, and placing his blowing-pipe across the two pieces of wood, which are exactly similar to the elbows of an arm chair, he rolls the pipe along the arms with his left hand, while he forms the glass vessel, which projects over the arm with the pliers held in the right hand. This operation is seen at the left hand of the vignette. At the same time that he holds the vessel in the plier D, as shewn in fig. 3, he turns it round by roliing the blowingiron. By this means it is made truly circular. The end is flattened to make the bottom of the decanter, by the flat blade of the pliers pressed against it, while it is turning round. It is to be observed, that the pliers or any tools which are to touch the glass, must be rubbed with bees-wax, or the cold metal would crack the glass. When these proceedings have brought the decanter to the state of fig. 3, the boy brings the rod B with a small portion of glass at the end; sticking it to the bottom of the vessel, the workman touches the neck with a piece of cold iron, and the glass instantly separates from the blowing-pipe. The boy then heats the glass at the furnace mouth; and when he returns it the workman opens the mouth of the decanter with the point of the pliers, as at fig. 5. The rings on the neck are put on by the boy bringing a piece of hot glass, a, fig. 6, and rolling it round the neck: then cutting it off by the shears E, and smoothing it by the pliers, the decanter is broken off from the rod B, and the operation is completed. Another boy now carries it by putting a long stick into the mouth, and thus conveys it into the top compartment of the furnace over the vault. The manner of doing this is shewn at the left-hand side of the furnace. Here the glass remains several hours at a considerable heat, until it is thoroughly annealed, and loses that brittleness which it would have without such an operation. A common glass bottle for wine is first brought to the state of K, fig. 7. This is placed in the mould GH, the two halves of which are shut down together, and the ring b put over the handles kk to keep it shut. The workman then blows through his tube B, and inflates the glass so as to fill the mould: by this means all the bottles will be of one size.
Watch glasses are made by first blowing a hollow globe, the proper radius for the glasses; then by touching it with the iron ring, fig. 8. This cracks out a watch-glass in an instant. The same globe will make several glasses.
Window or table-glass is worked nearly in the manner above described: the workman blows and
manages the metal, so that it extends two three feet in a cylindrical form. It is then ca ried to the fire, and the operation of blowing 1 peated till the metal is stretched to the dime sions required, the side to which the pipe is fixed diminishing gradually till it ends in a pyramidal form; but, in order to bring both ends nearly to the same diameter, while the glass continues flexible, a small portion of hot metal is added to the pipe; the whole is drawn out with a pair of iron pincers, and the same end is cut off with a little cold water as before.
The cylinder thus open at one end is returned to the mouth of the furnace, where it is cut by the aid of cold water, after which it is gradually heated on an earthen table, in order to unfold its length, while the workman with an iron tool alternately raises and depresses the two halves of the cylinder.
Plate-glass is the last and most valuable kind, and is thus called from its being cast in plates or large sheets: it is almost exclusively employed for mirrors or looking-glasses, and for the windows of carriages.
Plate-glass was formerly blown; but that method having been found very inconvenient, casting was invented; namely, the liquid metal is conveyed from the furnace to a large table, on which it is poured, and all excrescences, or bubbles, are immediately removed by a roller that is swiftly passed over it. It is then annealed in the manner already referred to.
GLASS (Painting in). The ancient manner of painting in glass was very simple: it consisted in the mere arrangement of pieces of glass of different colours in some sort of symmetry, and constituted what is now called Mosaic work. (See MoSAIC). In process of time they came to attempt more regular designs, and also to represent figures heightened with all their shades: yet they proceeded no farther than the contours of the figures in black with water-colours, and hatching the draperies after the same manner on glasses of the colour of the object they designed to paint. For the carnation they used glass of a bright red colour; and upon this they drew the principal lineaments of the face, &c. with black. At length, the taste for this sort of painting improv ing considerably, and the art being found applicable to the adorning of churches, palaces, &c. they found out means of incorporating the colours in the glass itself, by heating them in the fire to a proper degree, having first laid on the colours. A French painter at Marseilles is said to have given the first notion of this improvement, upon going to Rome under the pontificate of Julius II.; but Albert Durer and Lucas of Leyden were the first that carried it to any height.
This art, however, has frequently met with much interruption, and sometimes been almost totally lost; of which Mr. Walpole gives the following account in his Anecdotes of Painting in England: "The first interruption given to it was by the reformation, which banished the art out of churches; yet it was in some manner kept up in the escutcheons of the nobility and gentry in the windows of their seats. Towards the end of queen Elizabeth's reign, indeed, it was omitted even there; yet the practice did not entirely cease. The chapel of our Lady at Warwick was ornamented anew by Robert Dudley earl of Leicester and his countess, and the cipher of the glass-painter's name yet remains, with the date 1574; and in some of the
at Oxford the art again appears, dating à 1622, by the hand of no contemptible
ould supply even this gap of 48 years by many dates on Flemish glass: but nobody ever supposed that the secret was lost so early as the reign of James I.; and that it has not perished since will be evident from the following series, reaching to the present hour.
"The portraits in the windows of the library at All Souls, Oxford. In the chapel at Queen's College there are twelve windows, dated 1518. P. C. a cipher on the painted glass in the chapel at Warwick, 1574. The windows at Wadham-college; the drawing pretty good, and the colours fine, by Bernard Van Linge, 1622. In the chapel at Lincoln's Inn, a window, with the name Bernard 1623. This was probably the preceding Van Linge. In the church of St. Leonard, Shoreditch, two windows by Baptista Sutton, 1634. The windows in the chapel at University-college, Henry Giles pinxit 1687. At Christ-church, Isaac Oliver, aged 84, 1700. Window in Merton-chapel, William Price, 1700. Windows at Queen's Newcollege, and Maudlin, by William Price, the son, now living, whose colours are fine, whose drawing is good, and whose taste in ornaments and Mosaic is far superior to any of his predecessors; is equal to the antique, to the good Italian masters, and only surpassed by his own singular modesty.
"It may not be unwelcome to the curious reader to see some anecdotes of the revival of taste for painted glass in England. Price, as we have said, was the only painter in that stile for many years in England. Afterwards one Rowell, a plumber at Reading, did some things, particularly for the late Henry earl of Pembroke; but Rowell's colours soon vanished. At last he found out a very durable and beautiful red; but he died in a year or two, and the secret with him, A man at Birmingham began the same art in 1756 or 1757, and fitted up a window for lord Lyttleton in the church of Hagley, but soon broke. A little after him, one Peckitt at York began the same business, and has made good proficiency. A few lovers of that art collected some dispersed panes from ancient buildings, particularly the late lord Cobham, who erected a Gothic temple at Stowe, and filled it with arms of the old nobility, &c. About the year 1753 one Asciotti, an Italian, who had married a Flemish woman, brought a parcel of painted glass from Flanders, and sold it for a few guineas to the hon. Mr. Bateman of Old Windsor. Upon that I sent Asciotti again to Flanders, who brought me 450 pieces, for which, including the expence of his journey, I paid him 36 guineas. His wife made more journeys for the same purpose; and sold her cargoes to one Palmer, a glazier in St. Martin's-lane, who immediately raised the price to one, two, or five guineas for a single piece, and fitted up entire windows with them, and with mosaics of plain glass of different colours. In 1761 Paterson, an auctioneer at Essex-house in the Strand, exhibited the two first auctions of painted glass, imported in like manner from Flanders. All this manufacture consisted in rounds of scripture-stories, stained in black and yellow, or in small figures of black and white; birds and flowers in colours, and Flemish coats of arms."
The colours used in painting or staining of glass are very different from those used in painting either in water or oil colours. For black, take scales of iron, one ounce; scales of copper, one ounce; jet, half an ounce; reduce them to
powder, and mix them. For blue, take powder of blue, one pound; nitre, half a pound; mix them and grind them well together. For carnation, take red chalk, eight ounces; iron scales, and litharge of silver, of each two ounces; gum arabic, half an ounce; dissolve in water, grind all together for half an hour as stiff as you can; then put it in a glass and stir it well, and let it stand to settle fourteen days. For green, take red lead, one pound; scales of copper, one pound; and flint, five pounds; divide them into three parts, and add to them as much nitre; put them into a crucible, and melt them with a strong fire; and when it is cold powder it, and grind it on a porphyry. For gold colour, take silver, an ounce; antimony, half an ounce; melt them in a crucible; then pound the mass to powder, and grind it on a copper plate; add to it yellow ochre, or brick-dust calcined again, fifteen ounces, and grind them well together with water. For pur. ple, take minium, one pound; brown stone, one pound; white flint, five pounds; divide them into three parts, and add to them as much nitre as one of the parts; calcine, melt, and grind it as you did the green. For red, take jet, four ounces; litharge of silver, two ounces; red chalk, one ounce; powder them fine, and mix them. For white, take jet, two parts; white flint, ground on a glass very fine, one part; mix them. For yellow, take Spanish brown, ten parts; leafsilver, one part; antimony, half a part; put all into a crucible, and calcine them well.
In the windows of ancient churches, &c. there are to be seen the most beautiful and vivid colours imaginable, which far exceed any of those used by the moderns, not so much because the secret of making those colours is entirely lost, as that the moderns will not go to the charge of them, nor be at the necessary pains, by reason that this sort of painting is not now so much in esteem as formerly. Those beautiful works, which were made in the glass-houses, were of two kinds.
In some, the colour was diffused through the whole substance of the glass. In others, which were far the most common, the colour was only on one side, scarce penetrating within the substance above one-third of a line; though this was more or less according to the nature of the colour, the yellow being always found to enter the deepest. These last, though not so strong and beautiful as the former, were of more advantage to the workmen, by reason that on the same glass, though already coloured, they could show other kinds of colours where there was occasion to embroider draperies, enrich them with foliages, or represent other ornaments of gold, silver, &c.
In order to this, they made use of emery, grinding or wearing down the surface of the glass till such time as they were got through the colour to the clear glass. This done, they applied the proper colours on the other side of the glass. By these means, the new colours were hindered from running and mixing with the former, when they exposed the glasses to the fire, as will appear hereafter. When indeed the ornaments were to appear white, the glass was only bared of its colour with emery, without tinging the place with any colour at all; and this was the manner by which they wrought their lights and heightenings on all kinds of colour.
The first thing to be done, in order to paint or stain glass in the modern way, is to design, and even colour the whole subject on paper. Then they choose such pieces of glass as are clear, even,
and smooth, and proper to receive the several parts; and proceed to distribute the design itself, or the paper it is drawn on, into pieces suitable to those of the glass, always taking care that the glasses may join in the contours of the figures and the folds of the draperies; that the carnations and other finer parts may not be impaired by the lead with which the pieces are to be joined together. The distribution being made, they mark all the glasses as well as papers, that they may be known again which done, applying every part of the design upon the glass intended for it, they copy or transfer the design upon this glass with the black colour diluted in gum-water, by tracing and following all the lines and strokes as they appear through the glass with the point of a pencil.
When these strokes are well dried, which will happen in about two days,the work being only in black and white, they give it a slight wash over with urine, gum arabic, and a little black; and repeat it several times, according as the shades are desired to be heightened; with this precaution, never to apply a new wash till the former is sufficiently dried. This done, the lights and risings are given by rubbing off the colour in the respective places with a wooden point, or the handle of the pencil.
As to the other colours above mentioned, they are used with gum-water, much as in painting in miniature; taking care to apply them lightly for fear of effacing the outlines of the design; or even, for the greater security, to apply them on the other side; especially yellow, which is very pernicious to the other colours, by blending therewith. And here too, as in pieces of black and white, particular regard must always be had not to lay colour on colour, or put on a new lay, till such time as the former is well dried.
When the painting of all the pieces is finished, they are carried to the furnace to anneal or bake the colours. See ENAMELLING.
Having often been delighted with the grand effect produced by the windows of stained glass in old churches and monasteries, we have regretted that such fine and durable colouring should, in so many cases, have been prostituted upon wretched designs inferior to the productions of our sign-post daubers. We have wished that some mode could be devised of copying and multiplying pictures upon glass-some mechanical mode, which should require the aid of the artist in the first instance only, and leave all the subsequent operations to be performed by inferior hands, as in the case of copper-plate printing. Portraits at least, on a single piece of glass, which should perpetuate the features of great men and beautiful women, secure from that decay of colour and of canvas which has already began to obliterate the finest paintings of the greatest artists whom the world has ever produced, might possibly be produced in the following way:
Suppose, after the outline of a likeness is drawn, that blocks were cut from it after the same manner as for calicoes, or paper-hangings, only with superior nicety, and in greater number for the purpose of multiplying and better blending the tints.
the different blocks, to unite into a complete whole, let the paper be placed under a frame secured in an immoveable position during the operation. The blocks being accurately squared, all exactly of the same dimensions, and each nicely fitting the frame, cannot, in passing through it to deliver their veral impressions, make the smallest deviation from their intended places, but must produce an exact picture at least on the paper.
To transfer that impression to glass, is, indeed, a work of nicety and difficulty. Were it not for some smaller strokes which must necessarily be in wood, the entire impression might in the outset be made on the glass itself, without any intervention of paper; since experience has proved to the calico-printers that the great masses of colour cannot be successfully delivered from wood; wherefore they are obliged, in those parts of their patterns, to use bits of smooth worn-out beaver-hat, which might very well be pressed on the glassplate.
However, from what we every day see effected in the case of prints affixed to glass without any of the paper remaining, and also of copper-plate embellishments upon porcelain and queen's ware, we doubt not that the picture, while fresh, may, by well-managed pressure, be transferred from the paper to an even plate of ground glass coated with a proper gluten which shall not, at least not materially, ofiuscate its transparency; and experi ment must determine whether the paper may afterward be gently drawn or peeled off, or must be burned away, or destroyed by a corrosive liquid, if any such can be found, which will not injure the colours.
Suppose, however, the operation of removing the paper to be satisfactorily performed, proceed we now to secure the indelibility of the picture.
Let a square plate of cast-iron, an inch or two in thickness, and as level and smooth as possible, be furnished on every side with a metal ledge rising an inch or more in height, which ought to be in two separate pieces, the one permanently fastened to the plate, the other capable of being removed at pleasure, for the purpose of laying in and taking out the glass without violence.
Within that ledge let the glass be fitted closely touching it on every side, and lying with the painted surface uppermost. Upon this lay another plate of glass, fitted in the same manner.
Let, now, the metal frame, with the inclosed glasses, be exposed to the action of fire until the glass plates, without being melted to absolute fluidity, shall nevertheless become sufficiently soft to coalesce into one body under a strong pressure. The body which conveys the pressure, and lies in immediate contact with the glass, must equally fit and completely fill the entire space between the ledges, that there be no room for the soft glass to spread in any direction.
Those who have witnessed the process pursued in softening tortoise-shell in the fire, and pressing it into the various shapes of snuff-boxes, étuis, &c. &c. will not conceive much difficulty in this use of the glass. It may be managed by the aid of a machine somewhat similar to, but more powerful than, a common printing-press, with a solid metal platine, to fit and fill the frame, as above; though much better contrivances may be found among the multifarious engines employed at Birmingham for the purposes of coining, and striking the heavy dies, than any we can possibly suggest. In whatever manner the two glasses may be pressed into union, the united body may be afterward ground and polished.