GLAZING OF WINDOWS.

Before proceeding to speak of glazing, the order in which its various processes present themselves naturally demands that we should say something of putty.

This important and indispensable article in the glazier’s trade is composed of whiting and linseed oil. Chalk is sometimes used instead of the former, but the expense and labour incurred in preparing it is much greater, and besides it is generally mixed with sand, so that it is no object to the glazier to employ it. Whiting is in every way to be preferred; it must be thoroughly dried before the oil is added to it, otherwise the union will not be effected, or at least it will be very imperfect.

After the whiting has been thoroughly dried and prepared, it ought to be passed through a very fine sieve, and all the lumps and knots that remain pulverised, and then also passed through the sieve. Great care must be taken to keep the whiting free of sand and other extraneous substances.

When putty is to be made, put the proper quantity of oil into a tub or other open vessel, and gradually add the whiting whilst yet in a hot state, at the same time keeping the whole in motion with a stick, until it becomes of a sufficient consistency to admit of being wrought by the hand on a board or table. Having been removed thither from the tub, it must be wrought up with dry whiting, until it is converted into a solid compact mass. When brought to this state, it ought to be put into a hollowed stone or mortar, and beat with a wooden mallet till it becomes soft and tenacious, when more whiting must be added, until it has attained a proper consistency.

It is considered that the putty is improved if the whiting and oil, after being mixed, are allowed to remain for about twenty hours before being wrought up. After putty has been made, it should be firmly packed in a cask, from which it may be taken from time to time, as it is required. It ought not to be used for ten or twelve days after it is made, when its colour, from having at first been a dull yellow, will have changed to a whitish free-stone, which renders it more suitable for most purposes. After a lapse of six or eight weeks, the putty in the cask will become hard; but it is easily restored to its original softness, by being beat as before, and it is much improved by this second operation.

Putty is made in England in large quantities, and is ground in a mill in the same way as white lead; but this is no improvement, βs it is generally overwrought in this method of preparation, and rendered so tough and tenacious that it does not work well, and is entirely without that degree of pliability which putty ought to possess.

When putty is required of a superior degree of fineness, and which will also dry quickly, add a little sugar of lead, or litharge; and if an increase of strength be wanted, a little white lead.

We now proceed to glazing.

To glaze well, neatly, and expeditiously, simple as the operation may appear, is an art for the thorough acquirement of which many years of practice are necessary.

When a glazier receives an order to glaze a house, he must first, of course, proceed to measure the work to be done. In doing this, he must take the full size of the panes, that enough may be left for stripping, so as to produce an accurate fit into the sashes. This fitting must be performed with great care and nicety, leaving about one thirty-second part of an inch of space on each side and end of the pane, between it and the check. In other words, the pane must fill the space appropriated for it, to within the thirty-second part of an inch, or thereabouts.

This space is left to provide for such occurrences as the wood swelling with moisture, or the building setting, in which cases the panes would be apt to crack.

When the panes have been fitted into the checks of the sashes in the manner spoken of, they must be removed, and the checks well bedded with beat putty. This done, the panes are again returned to their places, and gently pressed or lodged into the bedding, the workman, as it were, humouring the glass should it be bent or twisted, and taking care that there is no hard extraneous substance mingled with the putty, which might endanger, if not actually break, the glass. When a pane is perfectly bedded it lies quite firm, and does not spring from the putty; but when, either from a perverse bend or twist in the glass, or any other accidental cause, it happens that it cannot be made to go quite close to the check, the vacant space must be carefully and neatly filled upon the back puttying, otherwise the window will not be impervious to the weather, and will be very apt to fall into decay by the admission of moisture.

It may not be superfluous to observe here, that the convex or round side of the pane, where such a shape occurs, should be presented to the outside, and the concave or hollow to the inside. The reasons for recommending this disposition of such panes are so obvious that they need hardly be enumerated. It may, however, be stated generally, that when thus placed, they resist the weather better than if the hollow sides were exposed to it.

After the pane has been bedded, the next process is the [7:10:575]outside puttying. This putty should be kept in the fore check, about the thirty-second part of an inch below the level of the inside check, so as to allow the thin layer of paint which binds these two substances together to join the putty and glass; and that it may not offend the eye by being seen from the inside; and that, when it is painted, the brush may not encroach on any visible part of the pane, leaving those ragged lines or marks which are so often seen from the inside on ill-finished windows, and which are so displeasing to the eye. This operation, and finishing the corners, are two nice points in the. art, and therefore, when properly done, discover the neat-handed and skilful tradesman.

It is the opinion of some experienced glaziers, that the inside puttying, which is the next process, ought to be allowed to remain eight days before being finished off, while others, again, say that this should be immediately done. The experience of the writer inclines him to the former opinion. By standing over for some little time, the putty acquires a hardness which admits of a better and neater finish than when it is in the soft working state, and in this way also it is not liable to shrink. Of course this is only recommended in cases of extensive jobs. When only a few panes are done, it is better to finish them off at once, than subject the employers to the inconvenience of a second visit from the glazier for so trifling a purpose.

When the finishing does take place, however, the putty must be cut clean off with the putty knife, and on a level with the style of the astragals. Complete the work by cleaning the glass and putty with a 000 duster brush, which removes all dust and loose putty from the pane, lightly and effectually.^[1. In taking out old glass from windows, the cold putty knife is used; but when the putty has been in the windows for ten or twelve years, it becomes nearly as hard as stone, and impenetrable to the knife. In this case there are various means used to extract !k κ ∕m∙ , n wki hTh ι the ≡PPbcation of hot iron to the putty is sometimes adopted; but this cannot with safetv he applied to the bedding, to which the glass obstinately adheres. Muriatic acid diluted with water is an excellent means of removing putty from g ⅛ the f™me?»iXn S rthi ed by . rubbing the P utt 5 occasionally with a bit of stick. The most effectual wav to remove the' glass, then-nnfsnľľnrXZΣIwΓĩ and . t . he S' ass valuable, is to put the frames into a horse dunghill, keeping the whole damp (if the weather is not so) for several weeks, which completely loosens the glass, and rots or destroys the frames. ] Hot-House Glazing. — The frames or sashes of a hothouse ought, before being glazed, to receive two coats of white paint, to which a small portion of red lead has been added to facilitate its drying, and to give increased strength and durability to the paint.

The panes in the roofs of hot-houses are generally of either of three forms; the first is the square pattern; the second is the tapered, that is, terminating in an obtuse angle; and the third the semicircular. The first is most generally used; the second is considered an improvement on the first, in so far as the tapered point carries off the rain down the centre of the pane, and thereby preserves the astragals; but there is a loss in shaping the glass to the tapered point. The third or semicircular is decidedly the best pattern of the three; the water is not only drawn to the centre of the pane, and the astragals protected from the rain, but this pattern has a more elegant appearance, when uniformly glazed, than either of the two other shapes. There is no loss in cutting the glass to the curve, and it is therefore not more expensive.

The dimensions of hot-house panes are generally about six inches, and are made to overlay each other, to an extent regulated by the circumstance of their being puttied at the overlay or not.

If it is intended to fill in the overlays with putty, they need not be more than a quarter of an inch in depth; but if it is not intended to putty them, they must then be at least five eighths of an mch.

The overlays, however, ought always to be puttied, and that for two reasons. First, because it will more certainly secure their being water-tight ; and because, in the next place, it will prevent the breakage to which the panes are liable from the freezing of the water, or moisture, which lodges in the overlay, and, expanding, shivers the glass in all directions; when they are filled with putty, such an accident cannot happen.

In glazing hot-house roofs, it must be observed, that the courses ought to run from end to end, and that the smaller panes, when such are used, should be reserved for the top.

When sashes are glazed, they ought to stand for eight or ten days before taking off the back putty, and they ought not to be painted for about three weeks afterwards, that the putty may consolidate. Great care, too, should be taken, when the sashes are newly glazed, that they be not in any way twisted or bent, as such an accident would almost inevitably start the panes from their beds, and thus render them pervious to water.

When sashes are of considerable dimensions, say about six feet by three, they should be strengthened by having two iron rods placed across them at equal distances, and screwed to the astragals. This will serve to prevent the accident of twisting, to which such frames are extremely liable, and which is very injurious to them after they have been filled with glass.

The putty used for glazing hot-houses ought to be of the very best description, as, from the circumstance of its position, it is necessarily more exposed to the action of the weather than in the perpendicular windows. The putty used for filling in the overlays ought to be of black or lead colour, which, as every glazier knows, is imparted to it by working it up with lamp-black; but as this substance has the effect of weakening the putty, the defect may be remedied by adding two pounds of white lead, ground in oil, to each stone of putty, and in a similar proportion to smaller or greater quantities. Indeed all putty used in glazing hot-houses ought to have a portion of white lead mixed with it, as it adds greatly to its strength.

Lattice or Lead Windows. — This antique and singularly beautiful style of glazing has unaccountably fallen much into disuse, although of late years it has certainly undergone something like a resuscitation, in consequence of a revival of the public taste for stained glass, and a growing predilection for Gothic architecture in churches, cottages, and the like. For these, and for staircase windows, and indeed all windows similarly situated, as in halls, lobbies, or the like, it is peculiarly adapted.

It may be proper to premise, that lead windows require stained or coloured glass for producing their fullest and best effects, and it was with stained glass only that they were originally constructed; but very neat and elegant windows are executed in this style with plain glass, where variety and beauty of figure are made to compensate foi the absence of colour

Lead windows may be made to any pattern, and in this there is great scope for the display of a correct taste. In the time of Elizabeth, this branch of the glazier’s art was carried to great excellence, especially by one Walter Geddes, who was employed in glazing most of the royal and public buildings of that period. This person executed in this style some windows of transcendent beauty, displaying an endless variety of the most elegant and elaborate figures. The most useful and most common description of plain glass lead windows, however, are those of the diamond or lozenge shape; but, as already said, they may be made to any pattern desired. The following are a few specimens of lattice windows. (See Plate [7:10:576]CCLXIX.) Fig. 1 is the east window of St Giles' Church, Edinburgh. Fig. 2 is a less imposing, but still a very chaste and beautiful, specimen of a lattice window. This has a beautiful effect by introducing stained glass into the long skittle-shaped pieces, and in the rosette in the centre. Fig. 3 represents the architecture of a window in Oxford Cathedral, filled with stained glass in the Gothic style.

The lead work can be adapted with ease to any pattern that may be chosen for the glass; and it can likewise be made to any breadth, from one eighth to five eighths of an inch. The one eighth, however, is only used for fancy work, and is not as yet much in demand; that which is most generally used is three-eighth lead. This width makes neater and better work than that of any other dimensions.

The glazier may purchase prepared leading for windows in any quantity; but he will produce it himself at half the cost, and probably more to his own satisfaction. The apparatus and tools necessary for doing this are, a glazier’s vice, or lead mill, moulds for casting the lead into slender bars or rods of about eighteen inches in length, which is the first process; a three-fourth inch chisel; a hard-wood fillet for forcing the glass into the grooves in the lead frame-work; and an opener or wedge tool, made also of hard wood, or ebony, for laying open the grooves for the reception of the glass; two copper bolts for soldering, the end formed like an egg. A correct delineation of the vice or mill alluded to is given in Plate CCLXX. in describing which, in its various connected parts, the same letters of reference are adapted to the different figures, so far as necessary, which, with the isometrical views, will facilitate the comprehension of their parts and properties.

Fig. 1, an end view, partly open, of a mould for casting three varieties of patterns, which are thus prepared for being forced through the machine. By an ingenious construction of the handle, it is made to lock and unlock by inclined planes, acting on studs, aa. Fig. 2, a side view, also partly open; and fig. 3, an isometrical view of the mould prepared for pouring in the metal.

The metal or cast being removed from the mould, a pair of the dies (one only of each pair is represented), according to the pattern required, figs. 4, 5, 6, 7, are placed in the machine, as seen at cc, fig. 8, isometrical view. After they are put in, a thin iron cover (b, fig. 10), with an oblong hole in the middle, is put on to guide the metal into the rollers. Figs. 9,10, and 11, represent three views of the machine as prepared for operating. In figs. 9 and 11, the metal, dd, is represented passing through the machine, which is accomplished by turning the winch handle, ee, acting on two equal sized toothed wheels, ff. On the axles of these are two rollers, gg, slightly serrated (dotted through in figs. 8 and 10); these rollers draw the metal through, while the dies give the desired form. To allow the axles and rollers to be placed in the frame or body of the machine, A, the cover, A, is removed by unscrewing the bolt, i, figs. 8, 10, 11. The toothed wheels, fj', are also taken off, by unscrewing the nuts, A∕c. The tempering screw bolt, I, is for adjusting the dies after they are put iħ their place. The screw bolts, mm, are for fixing the machine to a table or bench.

Fig. 12 is an isometrical view of the cover, A, removed to show the ports, nn, through which the axles of the rollers pass.

Fig. 13 shows the shape of the bolt used for soldering the lead windows, and fig. 14 the opener already described.

The lead intended to be employed in window making must be sqft, and of the very best quality; and great care must be taken to have the moulds properly tempered, otherwise the lead will not be equally diffused in them, and the castings consequently not perfectly solid throughout, as they ought to be.

If this is not attended to, that is, if the castings are not perfectly solid, they will come out of the mill, to which they are presented after being taken from the moulds, all fretted on the edges, and thus in a state totally unfit for the purpose for which they were intended.

The castings are, as already noticed, usually about eighteen inches in length, and are afterwards extended by the mill represented by the figure above, to the length of five or six feet.

It may not be unnecessary to add, that the mill not only extends the lead, and reduces it, at the pleasure of the operator, to the dimensions required, but at the same time forms the grooves into which the edge of the glass is afterwards introduced in forming the window.

When the lead has been prepared in the manner described, the glazier ought to proceed to cut out the panes wanted. For this operation he must prepare by first outlining the full dimensions of the window, and then lining it off to the pattern required, shaping the panes accordingly. If the window is of a large size, this may be done by compartments, to be afterwards united, and thus be more conveniently wrought. Great accuracy must be observed in cutting the panes, or a very irregular panel will be produced, as those lines that ought to be parallel or otherwise will not be correctly so, which will greatly injure the appearance of the work.

When all the glass has been cut for the window, the next thing to be done is to open the grooves in the lead with the opener or wedge tool. The panes are then, in order that they may be water-tight, fastened very firmly into the grooves with the wooden fillet already spoken of (which may be fixed on the handle of the chisel or cutting tooD, the parallel lines of lead being secured in their proper places on the board, when the window is of the diamond shape, by a small nail at either end, until the course is finished, when the work is permanently fastened by running a small quantity of solder gently over the two connecting pieces of lead at each joint, or angular point. When the window has been completed, it should be removed from the working board to a flat table, and there covered with a thick layer of cement, composed of white lead, lamp black, red lead, litharge, and boiled linseed oil, with a half-worn paint brush, and the composition carefully rubbed into every joint. This will render the window completely impervious to the weather, as the cement, if properly laid on, will fill every chink, where it will soon become as hard and durable as any other of the materials of which the window is composed. When this operation has been completed, clean the window with a cloth and whiting. Should the outside be wanted black, omit the blacking in the first compost; and finish by laying on the lamp black with a polishing brush.

The window, on being fitted into the frame, that is, on ' being set in its place in the building for which it is intended, ought to be supported with three-eighth inch iron rods, extending three eighths of an inch beyond the breadth of the frame on each side, running across it at the distance of from twelve to fourteen inches from each other, and secured to the lead frame-work at intervals, either with copper wire, or lead bands manufactured by the mill. These rods, for obvious reasons, ought to be so arranged as to intersect the window exactly at the terminating point of a row of the diamonds. For instance, if the diamonds are each six inches in length or height, the first rod ought to intersect the window at the top of the third row, or eighteen inches from the bottom of the frame, and so on, until the window be equally divided in this way throughout its whole length. If the diamond, again, be only three inches in length, then the first rod ought to pass at the top of the fourth row, or twelve inches from the bottom, this proportion of distance being, of course, maintained throughout. The usual distance is fourteen inches, but this must be regulated by the [7:10:577]breadth of the window between the mullions. If themul-lions are of stone, the grooves in which the window is set ought to be filled up with Roman cement, or mastic. If of wood, with oil putty.

THE CUTTING DIAMOND.

Before the introduction of the diamond as an agent in cutting glass, that operation was performed by means of emery, sharp pointed instruments of the hardest steel, and sometimes red-hot iron. These were the only contrivances known and practised by the ancient glaziers.

In considering the diamond in its relations to the purposes of the window-glass cutter, there occur some circumstances not unworthy of remark. Amongst these, it may be noticed, that the cutting point of the diamond must be a natural one; an artificial point, however perfectly formed, will only scratch the glass, not cut it. The diamond of a ring, for instance, will not cut a pane, but merely mark it with rough superficial lines, which penetrate but a very little way inwards. Artificial points, comers, or angles, therefore, produced by cutting the diamond, are adapted only for writing or for drawing figures on glass, and such were those used by Schwanhard, Rost, and the other old artists who were celebrated for ornamenting glass vessels. The cutting diamond does not write so well on glass, from the circumstance of its being apt to enter too deeply, and take too firm a hold of the surface, and thus become intractable. It may further be noticed, that an accidental point produced by fracturing the diamond, is as unfit for cutting as an artificial one. Such a point will also merely scratch the glass. No point, in short, that is not given by the natural formation of the mineral, will answer the purposes of the window-glass cutter.

The large sparks, as the diamonds used for cutting glass are called, are generally preferred to the small ones, from the circumstance of their being likely to possess, although this is by no means invariably the case, a number of cutting points; while the very small sparks are not always found to possess more than one. Thus, if the point of the latter is worn or broken off, although the spark be turned, and reset in its socket, it will still be without the power of cutting, and consequently useless, while the former, on undergoing the same operation, will present a new and effective point.

The large sparks are called mother mark», and are sometimes cut down into as many smaller fragments bearing the same name, as there are natural points in them. Each of these, therefore, can have only one cutting point, and are consequently only proportionately valuable to the glazier, since they cannot be restored by resetting.

The Setting of Diamonds is a process with which every glazier ought to be acquainted; nor is it an art of difficult acquirement; some practice, and a little patience, are all that is necessary.

After having selected a stone, as clear and pellucid as possible, resembling a drop of water, and of an octoedrical shape, or as near to that form as it can be procured, the workman proceeds to ascertain which is its cutting point, or, if it has more than one, which is the best. This will be found to be that point which has the cutting edges of the crystal placed exactly at right angles to each other, and passing precisely through a point of intersection made by the crossing of the edges.

He then provides a piece of copper or brass wire, a quarter of an inch in diameter, having a hole drilled in one of its ends large enough to contain three fourths of the diamond to be set. Having temporarily secured the diamond in this hole, the setter ascertains the cutting point, by trying it on a piece of glass; and when he has discovered it, he marks its position by making a slight notch in the wire with a file or otherwise, exactly opposite to the cutting point, as a guide to him in his operations when he comes to fix it permanently in the socket head of the handle. When doing this, care is taken to keep it exactly parallel with the inclined plane of the socket head.

The cutting point having been ascertained, and the diamond fixed into its place, the wire is then cut off about a Quarter of an inch below the diamond, and filed down to ht exactly into the aperture in the socket head, into which it must be soldered. The rough or superfluous metal around the stone is removed with a file; and, lastly, the setting is polished with emery or sand paper. Such is the most approved method of setting new diamonds, and it applies equally to the resetting of old ones. But in the latter case, the first process, that of detaching the stone from its bed, is accomplished either by means of a knife, or by applying the blowpipe.

The art of managing the diamonds in glass-cutting, so as to produce effective results, can only be attained by considerable experience. The diamond must be held in a particular position, and with a particular inclination, otherwise it will not cut, and the slightest deviation from either renders an attempt to do so abortive. In the hands of an inexperienced person, it merely scratches the glass, leaving a long rough furrow, but no fissure. The glazier judges by his ear of the cut made. When the cut is a clean and effective one, the diamond produces, in the act of being drawn along, a sharp, keen, and equid sound. When the cut is not a good one, this sound is harsh, grating, and irregular. On perceiving this, the operator alters the inclination and position of his diamond, until the proper sound is emitted, when he proceeds with his cut.

Although the diamond cuts glass of an ordinary thickness with facility, it does not easily cut that which is of more than a medium thickness. In such cases, the desired division is effected by the application of a hot iron, which being brought in contact with the glass at certain points, produces a fissure in the direction required.

The diamonds employed in glass-cutting, are of the description known by the technical name of bort, a classification which includes all such pieces as are too small to be cut, or are of a bad colour, and consequently unfit for ornamental purposes. These are accordingly selected from the better sort, and sold separately, at an inferior price.

Though there are many substances that will scratch glass, the diamond was thought to be the only one that would cut it; but some experiments of Dr Wollaston have shown that this is not strictly correct. That eminent philosopher gave to pieces of sapphire, ruby, spinel ruby, rock crystal, and some other substances, that peculiar curvilinear edge which forms the cutting point in the diamond, and in which, and in its hardness, its singular property of cutting entirely lies, and with these succeeded in cutting glass with a perfectly clear fissure. They lasted, however, but for a very short time, soon losing their edge, although prepared at a great expense of labour and care; while the diamond comes ready formed from the hand of nature, and will last for many years.

MANUFACTURE or FLINT-GLASS OR CRYSTAL.

This is the species of glass of which the finest and most beautiful articles used for domestic purposes or for ornament are made. It is also largely employed in the manufacture of optical glasses, and for other philosophical purposes. It is the heaviest, the most brilliant, and also the most costly, of all the vitrified compounds. In order to convey an idea of the manufacture of flint-glass, we propose to give an account of a work in the vicinity of Edinburgh. Our description will be best understood by fire-quently[7:10:578] referring to Plate CCLXXI. Fig. 1 represents a cone twenty-two feet two inches in diameter at the bottom, ' eight feet diameter at the top, and sixty feet in height. It contains twelve arches^ α is a front view of one of them. Each of these arches contains one pot, and the whole of them are heated by means of flues which ramify round the whole cone, proceeding from one general furnace. The furnace, which is circular, is fifteen feet four inches in diameter, and six feet in height inside to the centre of the crown. Fig. 2 represents a pot which is manufactured of Stourbridge clay, of the best quality. From the bottom to the highest part the pot is thirty-eight inches in height, and the width outside thirty-four inches. The orifice of the pot measures about right inches across. About fourteen hours are necessary before the pots can all be filled, on account of the metal sinking into less bulk as it melts. During the whole time the furnace must be kept as hot as possible. After the pots are all filled, about forty-four hours elapse before the vitrified mass is brought to a proper state for working. More or less time is necessary according to the state of the materials, and from time to time the pots must be carefully scummed in order to remove any impurities.

As in every other branch of glass making, the proportions of the ingredients used for making flint-glass vary with almost every manufactory. The following is reckoned an excellent compound. Fine white sand, six hundredweights and a half; red lead or litharge (minium), three hundredweights and a half; calcined potash, two hundredweights; nitre, eighty-four pounds; manganese, from eight to eighteen ounces, according to circumstances; arsenic, from one to two pounds; cullet, or broken crystal, a quantity sufficient to fill up the pots. The above quantities of materials fill two pots.' On the authority of the Messrs Aikin,^[2. Dictionary of Chemistry, vol. i. p. 496. ] l a very excellent article may be made from 120 parts of fine white sand, forty parts wril purified pearl ash, thirty-five paru litharge, thirteen parts nitre, and a small quantity of black oxide of manganese. The principal difference between flint and other kinds of glass is in there bring present in its composition a considerable quantity of some metallic oxide. All metals in a state of oxidation will combine with silica and an alkali to form glass. Only lead and bismuth, however, can be employed in sufficient quantity so as to produce a bright colourless article. The other metals impart various hues to the mass. Lead being the cheapest of the two metals, is that universally employed. If it be used, however, in too great a quantity, it will not only tinge the glass of a yellow colour, but produce an inconveniently soft material.

After the metal has been brought to a state when it is fit for being wrought, the workmen commence operations. The implemenU which they use are few in number and simple in construction. The first tool required is a hollow iron tube between four and five feet in length, and one eighth of an inch in the bore; it is technically called the iron, and is dipped into the pot in the manner represented in Plate CCLXXI. figs. 5 and 6. After a sufficient quantity has been collected on the end of this rod, it is withdrawn from the pot and suspended for a few seconds in a perpendicular position, that the glass, which is at the under end, may be lengthened out beyond the rod. It is then rolled upon the marver. This process, by which the glass is rolled into a cylindrical form, is represented by fig. 7. The glass is now of a consistency to admit ņf its being blown into a hollow globe, as exhibited in fig. 8. The globe, however, not being rendered sufficiently thin by this first distension, it is repeated until the vessel has assumed the dimensions required. In every case of blowing, the pressure of the breath must be continued upon the tube for a short while, to prevent the globe from collapsing, which would be the case were the confined air allowed to escape. The external pressure would be greater than the resistance offered from within. If it is required to elongate the globe, this may be effected by dexterously whirling it in a circular manner through the air. The crystal is now in a fit state for lying horizontally upon the chair arms, as shown in figs. 9 and 10. The chair arms are merely two pieces of wood lying parallel to each other upon the workman’s seat or chair. The arm which lies next the heated metal is protected from injury by being covered with an iron plate. Another instrument, called a punty or “pontil,” is employed. This is a solid iron rod of a cylindrical shape, and smaller and lighter than the hollow tube at first used. A small quantity of melted glass is collected upon one end of this by an assistant, and applied to the end of the globe, as shown in fig. 9. The two masses of glass are thus united together, and that attached to the hollow tube is easily separated from it by touching it near to where the tube enters the globe, with a small piece of iron wetted with water. By this means the glass cracks, and a smart blow upon the iron tube completes the disunion. The workman now takes the punty from his assistant, and laying it upon the chair arms, rolls it backwards and forwards with his left arm, whilst with his right he moulds it into the various shapes required, by means of a very few simple instruments. By one of these, called a procello, the blades of which are attached by an elastic bow, like a pair of sugar tongs, the dimensions of the vessel can be enlarged or contracted at pleasure. Any superfluous material is easily cut away by means of a pair of scissars, glass when red hot being very easily divided. For smoothing and equalizing the sides of the vessel, a piece of wood, generally cedar, is used; and the workman is also furnished with compasses and graduated scale, to ensure the regularity in shape and size required. The article being finished, is detached from the punty in the same way as formerly, and weighed in a pair of scales to see that there has been the proper quantity of glass consumed in its manufacture. It is then carried by means of a pronged stick to the annealing oven, or lier as it is technically called.

The process of annealing is one of the last importance; because, were glass not properly annealed, it would crack with eyen very slight changes of temperature; see the article Annealing in this work. Plate CCLXXI. fig. 3, represents an annealing oven. It is simply a long, low, rectangular chamber, heated at one end, and provided with various shallow iron trays, which can be passed along the bottom of the chamber. Upon these trays the manufactured goods are put; and the lier pans, as they are successively filled, are pushed towards the colder end of the oven, from whence they are taken in a state little warmer than the temperature of the external atmosphere.

Glass Cutting The cutting, or rather the grinding of crystal, forms a distinct business in a flint-glass-house. In the manufactory before alluded to, steam power is employed to give motion to the machinery by which the process of cutting is effected. A shaft proceeding from the engine causes the revolution of several large drums, which run along each side of the cutting room. Upon these drums belts run, which proceeding upwards, pass over smaller wheels (such as a, fig. 4). By this means the cutting wheel b is made to revolve with great celerity. Opposite it the workman is placed, and applies to the surface of the wheel the article which is to be cut. Above the cutting wheel is a conical-shaped vessel c, made of wood, and filled with fine sand, which being moistened with water, runs [7:10:579]through upon the cutting wheel at the lower extremity, in a regular discharge. The hole in the bottom is of such dimensions, and so situated, as to admit the escape of the requisite quantity of moistened sand. Below the wheel is a vessel, ⅛ which receives the sand and water run down upon the wheel. Every one who has seen a crystal shop, must have remarked the infinitely varied appearances which the articles formed of flint-glass present. It is evident that, to produce these, the wheels must be of very various forms, broad, narrow, flat edged, mitre-edged, that is, having two faces, which form a sharp angle at their point of meeting, convex, concave, &c. They are made of iron both cast and malleable, of Yorkshire stone, and of willow wood. The iron wheels are used in the roughest part of the operations, and articles ground by these are further smoothed down by a wheel of Yorkshire stone. Wooden wheels are employed in the further smoothing and polishing of the crystal. For smoothing the surface, the edge of the wheel, is dressed with either rotten stone or pumice stone; and for imparting to it the highest degree of polish, putty powder is employed.

There are certain crystal shades in use for softening the light diffused by lamps. The process by which this lessening of the transparency is effected i» called frosting. The roughness is imparted to the inner, not the outer surface of the vessel; and it is done by the former being fixed in a lathe, and rubbed by a workman with a piece of wood covered with wet sand.

BOTTLE-GLASS·

Plate CCLXVΠI. fig. 4, is a ground plan, showing all the necessary buildings for two bottle-houses, and in one of the houses the ground plan of a four-pot furnace and ash arches. The furnace is an oblong square, similar to what we have described the crown-furnace to be, but arched over in the barrel shape. It is erected in the centre of the brick cone, above a cave, which admits the atmosphere to the grating. The working holes of this fumace, opposite each pot, for putting in the materials and taking out the liquid glass, are each about one foot in diameter. At each angle of the furnace there is also a hole about the same size communicating with the calcining arch, and admitting the flame from the main furnace, which reverberates on and calcines the materials in the arch. Fig. 1 shows the main furnace; 2, 3, 4, 5, the ash arches for calcining the materials; 6, 7, 8, 9, 10, 11, annealing arches; 12, two-pot arches; 13, what is considered an improved plan; 14, clay-house, for picking, grinding, sifting, and afterwards working the clay into paste for the purpose of manufacturing pots; 15, mill house for grinding clay; 16, a building containing a calcar furnace for experiments, or for preparing the materials, when the ash arch attached to the main furnace is under repair, including, 1, a sand crib, and 2, an ash crib for sifting and mixing the materials, sufficient for two houses.

The common green or bottle glass is made of the coarsest materials; sand, lime, sometimes clay, any kind of alkali or alkaline ashes, whose cheapness may recommend it to the manufacturer, and sometimes the vitreous slag produced from the fusion of iron ore. The mixture most commonly used is soap-maker’s waste, in the proportion of three measures to one measure of sand. The green colour of this glass is occasioned by the existence of a portion of iron in the sand, and, it may be. also in the vegetable ashes of which it is composed.

To distinguish it from flint-glass, which pays a higher duty, government does not allow the use of any but the coarsest kind of sea or river sand. When castor oil or champaigne bottles are wanted, a portion of crown-glass cullet is added, to improve the colour. The impurity of the alkali, and the abundance of fluxing materials of an earthy nature, combined with the intense heat to which they are subjected, occasion the existence of but a very small proportion of real saline matter in the glass; and thereby render it better than flint-glass for holding fluids possessing corrosive properties.

The soap-maker’s waste is generally calcined in two of the coarse arches, figs. 3 and 4, which are kept at a strong red heat from twenty-four to thirty hours, the time required to melt the materials and work them into glass, which is termed a journey. After the soap-maker’s waste is taken out of the arch, it is ground and mixed with sand in the proportions already mentioned. This mixture is put into the fine arches, and again calcined during the working journey, which occupies about ten or twelve hours more. When the journey is over, the pots are again filled with the red-hot materials out of the fine calcining arch. Six hours are required to melt this additional quantity of materials. The pots are again filled up, and in about four hours this filling is also melted. The furnace is then kept at the highest possible degree of heat, and in the course of from twelve to sixteen hours, according as the experience of the founder may determine, the materials in the pots are formed into a liquid glass fit for making bottles. The furnace is now checked by closing the doors of the cave, and the metal cooling, it becomes more dense, and all the extraneous matter not formed into glass floats upon the top. Before beginning to work, this is skimmed off in the way already described in our account of crown-glass making. A sufficient quantity of coals is added at intervals, to keep the furnace at a working heat till the journey is finished.

After the pots have been skimmed, the person who begins the work is the gatherer, who, after heating the pipe, gathers on it a small quantity of metal. After allowing this to cool a little, he again gathers such a quantity as he conceives to be sufficient to make a bottle. This is then handed to the blower, who, while blowing through the tube, rolls the metal upon a stone, at the same time forming the neck of the bottle. He then puts the metal into a brass or cast-iron mould of the shape of the bottle wanted, and, continuing to blow through the tube, brings it to the desired form. The patent mould now in use is made of brass, the inside finely polished, divided into two pieces, which the workman, by pressing a spring with his foot, opens and shuts at pleasure. The blower then hands it to the finisher, who touches the neck of the bottle with a small piece of iron dipt in water, which cuts it completely off from the pipe. He next attaches the punty, which is a little metal gathered from the pot, to the bottom of the bottle, and thereby gives it the shape which it usually presents. This punty may be used for from eighteen to twenty-four dozen of bottles. It is occasionally dipped into sand to prevent its adhering to the bottle. The finisher then warms the bottle at the furnace, and taking out a small quantity of metal on what is termed a ring iron, he turns it once round the mouth, forming the ring seen at the mouth of bottles. He then employs a shears to give shape to the neck. One of the blades of this shears has a piece of brass in the centre, tapered like a common cork, which forms the inside mouth; to the other blade is attached a piece of brass, used to form the ring. The bottle is then lifted by the neck on a fork by a little fellow about ten years of age, and carried to the annealing arch, where the bottles are placed in bins above one another. This arch is kept s little below melting heat, till the whole quantity, which amounts to ten or twelve gross in each arch, is deposited, when the fire is allowed to die out.

Such is a brief view of the various methods of manufacturing glass. The physical properties of this useful sub [7:10:580]stance will naturally fall to be treated of under the heads of the several sciences in which glass is employed.

The manufacture of glass is subjected to the excise laws; and the duties are not only very heavy, but the regulations for levying them are most complex and oppressive. The injuries which are inflicted upon trade by such a system of taxation are strikingly exemplified in the case of glass. In 1794, when the duty was L.l. Is. 5d. per cwt. for plate and flint, the other kinds being taxed in proportion, the quantities paying duty were as follow: Flint and plate, 67,615cwt j broad, 20,607; crown, 83,940; bottle, 227,467. The duties were successively raised, until in 1813 they amounted to L.4. 18s. The result of this was, that in 1816 the consumption had declined to, plate, 29,600; broad, 6140; crown, 55,502; bottle, 155,595.

In 1825 the duty was reduced one half, and the consumption rose to about what it was in 1794. But since the wealth and population of the country have more than doubled since that period, and as general luxury has been greatly extended, the manufacture of glass ought to have been nearly trebled. This would certainly be the case were the duties lowered or abolished. The following accounts show the pernicious influence of the existing duties:

I— Account of the number of Glass-Houses respectively employed in the Manufacture of Broad, Crown, Flint, Plate, and common Bottle Glass, in each year from 1829 to 1832 inclusive, in the United Kingdom.
[table]

II.— Account of the Quantities of Flint, Plate, Broad, Crown, and Bottle Glass, charged with the Duty in each year from 1829 to 1832 respectively, with the Rates of Excise Duty and Revenue accruing thereon.
[table]

III.— Account of the. Quantities of British-made Glass retained for Home Consumption, with the Imports of Foreign Glass entered for Home Consumption ; the Amount of Customs-Duty on the latter, and the Nett Revenue arising from British Glass, in each year from 1829 to 1832 both inclusive.
[table]

We can only notice a few of the regulations as to the manufacture of glass. Every glass-maker must take out an annual license, which costs him L.20 for each glasshouse; and he must make entry at the next excise-office, of all work-houses, furnaces, pots, pot-chambers, annealing arches, warehouses, and the like, under a penalty of L.200. Previously to the charging of the pots, twelve hours’ notice must be given in writing, of the time of beginning, the weiġht of metal, and the species of glass, on pain of L.50. If any material or preparation be put into a pot after notice has been given and a gauge taken by the officer, a penalty of L.50 is incurred; and if the manufacture be of flint-glass, the penalty is L.200. The officers are allowed to have access to the works at all hours by day and night, any attempt to obstruct them incurring a penalty of L.200; and the counterfeiting, altering, or effacing any marks made by them being visited with a penalty of L.500; connivance at its being done subjects the aggressor to a fine of L.200. The whole of the metal intended to be manufactured into common-glass bottles is to be worked within sixteen hours next after the same shall be begun; and when the bottles are put into the annealing arches, manufacturers are then, in the presence of the officer, to charge the pots with fresh materials, other than broken glass, not less than fifty pounds weight; and declarations are to be delivered in writing, of the number of such bottles, on penalty of L.100. Fraudulent weighing of glass is visited with a heavy penalty. Notices are not to be given for drawing out bottles, but only between eight o’clock in the morning and six o’clock in the afternoon. No crown-glass, German sheet-glass, or broad window-glass, can be manufactured beyond the thickness of one-ninth part of an inch, without being subjected to the duty paid on plate-glass. Such are a few of the laws and regulations, alike vexatious and impolitic, which have retarded the progress of glassmaking, and that too at a time when almost every other species of manufacture had far more than doubled itself. In fact, from the making of the pots themselves to the packing up of the glass for sale, every thing is done after a certain manner, which is determined by act of parliament. This being the case, how improvements are to be made in the art it is difficult to conceive. The laws which regulate the packing and exportation of glass are equally burdensome with those relative to its manufacture. The amount of drawback allowed upon this article will be seen from the table above given. (γ. γ. γ.) [7:10:581]Engraving on Glass. Professor Beckmann has proved, that, as early as the year 1670, the art of etching upon glass was discovered by Henry Schwanhard, son of George Schwanhard, who was a celebrated glass-cutter, patronised by the Emperor Ferdinand III. about the middle of the last century. At the time of his death, 1697, the father practised his art at Prague and Ratisbon. Whether the son followed the same business at the same towns, or removed to Nuremberg, is not very evident; but in the year above mentioned, some aqua-regia (nitre-muriatic acid) having accidentally fallen on his spectacles, he was surprised to find the glass corroded by it, and become quite soft. He thus, it is said, found himself in possession of a liquid by which he could etch writing and figures upon plates of glass.

But it is probable, as Beckmann seems to think, that he had discovered the fluoric acid itself; for in the year 1725 there appeared in a periodical work the following receipt for making a powerful acid, by which figures of every kind can be etched upon glass.

“When the spiritus nitri per distillationem has passed into the recipient, ply it with a strong fire, and when well dephlegmated, pour it, as it corrodes ordinary glass, into a Weidenberg flask. Then throw into it a pulverised green Bohemian emerald, otherwise called hesphorus (which, when reduced to powder, and heated, emits in the dark a green light), and place it in warm sand for twenty-four hours. Take a piece of glass well cleaned, and freed from all grease by means of a ley; put a border of wax round it, about an inch in height, and cover it all over with the above acid. The longer you let it stand so much the better; and at the end of some time the glass will be corroded, and the figures which have been traced out with sulphur and varnish will appear as if raised above the pane of glass.”

That the Bohemian emerald, or hesphorus, mentioned in this receipt, is green sparry fluor, cannot, says the professor, be doubted; and he seems to have as little doubt of the receipt itself having passed from Schwanhard and his scholars to the periodical work of 1725, from which it was inserted in the Oekonomische Encyclopadie of Krunitz. This supposition certainly acquires a considerable degree of probability from the similarity of Schwanhard’s method of etching to that which is here recommended, and which is so different from what is now followed. At present the glass is covered with a varnish either of isinglass dissolved in water, or of turpentine oil mixed with a little white lead, through which the figures to be etched are traced as on copper; but Schwanhard, when he had drawn his figures, covered them with varnish, and then by his liquid corroded the glass around them. His figures, therefore, when the varnish was removed, remained smooth and clear, appearing raised from a dim or dark ground; and Μ. Beckmann, who had persuaded some ingenious artists to make trial of this ancient method of etching, declares that such figures have a much better effect than those which are cut into the glass.

Burning Glass. See Burning Glass. Weather Glass. See Barometer. Musical Glasses. See Harmonica. Looking Glasses. See Mirror.