Chapter XIII: Miscellaneous Processes (1)

The various processes and details which have occupied the preceding chapters, are for the most part necessary to the production of every house. There are, however, many articles of iron and a few of brass employed in the interior and exterior fittings; but were we to enter into details respecting the iron manufacture, in order to show the modes of producing these articles, it would be difficult to confine this volume within reasonable limits. A few miscellaneous processes and details may, however, be collected in this chapter.

The principal metallic articles employed in the construction or permanent fittings of a house, are nails and screws; hinges; locks and keys; stoves and grates; bells, and the mechanism for hanging them; iron railings and bars; brass handles, plates, and other decorations; latches and fastenings, &c.

Nails.

_Nails_ are made of iron, either _cut_ by means of a machine into the tapering form which we call _cut brads_, or _wrought_ by means of hammers into the various forms of flooring nails, tacks, &c. _Screws_ are made by forcing a piece of iron wire into a cavity, the surface of which is cut into a spiral or screw-like form; this spiral cuts a similar spiral on the surface of the iron wire, which then becomes a screw; and one end of the wire is hammered or pressed down so as to form the _head_ of the screw. _Hinges_ of the commoner kinds are made by two flat pieces of iron, with a kind of projecting tube at one edge. These tubes are partially cut away, so that the two pieces may lap into each other; and a spindle or pin being passed down through both tubes, acts as an axis, on which both parts of the hinges turn. The more costly hinges require elaborate workmanship in their construction.

Locks and Keys.

_Locks_ and _Keys_ form a curious part of the hardware manufacture. The lock is made of a great many pieces, put together with screws. One part of it is always a moveable latch or bolt, which is capable, by tolerable force, of being thrust partially out through a hole in the side of the lock; and it is this bolt which, catching in a box or cell fixed to the door-post, secures the door to which the lock is attached. The object of the key is to act as a lever which shall move the bolt; and the great point of attention in the matter is, that no key or lever but one of a particular _size_ and _shape_ shall be able to move the bolt; herein is the security which we feel in a good lock. Wolverhampton and its neighbourhood is the great seat of the lock manufacture.

Stoves and Grates.

_Stoves_ and _Grates_ are made in a variety of forms. Their employment is obviously greatly dependent on the kind of fuel employed. In the kitchens of the old baronial residences, large logs of wood were thrown upon an immense stone or brick hearth, and there kindled. But when coals became commonly used in London and other great towns of England, about the year 1400, the use of some kind of stove or grate began to be felt, since the fuel was too valuable to be scattered on a wide-spreading hearth. From that time to the present, one continual series of improvements has taken place, having for their objects, to add to the elegance and neatness of a room, to facilitate culinary occupations, and to derive the greatest possible heat from a given quantity of fuel. It is only within a very few years that the principles regulating the last-mentioned circumstance have been at all well understood. Some parts of the metal for a grate or stove are produced by casting, others by forging, and others by rolling or pressing; and they are put together principally by rivets. For further details on this subject we refer to our seventh chapter.

Bells.

_Bells_ are, generally speaking, made of an alloy of copper and tin, which possesses more resonant qualities than most others. There is also a little ball or clapper suspended in the bell, which, by striking against it, produces the same effect as the hammer which strikes the outside of a church bell. The bell is generally fixed in a different part of the house from the handle with which it is rung, and the connexion between them is made by means of copper wire. As the wire has to turn round many corners and angles, it is fixed, at each corner to a _crank_, which is a kind of hinge or lever, so contrived as to transfer motion in a new direction at right angles to the former. Considerable care is required on the part of the bell-hanger, to prevent the wire from becoming entangled or interrupted in its free communication from the handle to the bell.

Brass Handles, Ornaments, &c.

Those are produced by _turning_, by _casting_, by _stamping_, or by _drawing_. In the first mode, the article is placed in a lathe, and turned by tools made of hard steel: in the second mode, melted brass is poured into moulds formed generally of sand, by which any desired form is produced: in the third mode, two stamps, one called a _matrass_ and the other a _die_, are cut or moulded to similar figures; a piece of sheet brass is laid on the matrass or lower stamp, the die or upper stamp is laid on the brass, and a powerful blow, either from a hammer, or from machinery, forces the brass to assume the form given to the two stamps. By the last mode, a slip of thin brass is forcibly drawn between two rollers, whose surfaces are indented with the requisite device, which device is thereby impressed on the bars. In one or other of these ways, most of the brass-work in our houses is made.

_Iron railings_ and _bars_ of various kinds are made either by forging or casting, and do not call for further notice here.

Preservation of Timber.

In our notices of the timber which enters into the construction of a house, no mention was made of the existing methods of preparing it so as to resist the action of dry rot and other decomposing agencies. Timber so prepared is not in very general use in house-building, and hence the notice of it occupies a more fitting place in the present chapter.

Vegetable matter, in common with all organic substances, is subject to decomposition and decay, as soon as life becomes extinct; and although the process is comparatively slower in its commencement and progress in vegetable than in animal matter, it is not, under ordinary circumstances, the less certain. During the existence of a plant, its various organs, under the influence of the mysterious principle of life, perform their respective functions in a manner similar to that of which we are more readily conscious in the animal frame. The plant absorbs its food from the soil and the surrounding air; it digests that food under the influence of respiration, and prepares rich and nutritive juices which circulate throughout its whole vegetable frame, and deposit materials of growth wherever they are wanted; it sheds its leaves in autumn, undergoes a season of torpor, and again becomes active and vigorous; thus it is clad in fresh leafy honours in the following spring. All this is the effect, or rather the result, of vitality. The plant dies, and then its constituent parts gradually assert their individual existence, and resume their original affinities. Some pass into the air; some form new compounds; and others, which during the life of the plant ministered to its healthy action, now work energetically and destructively on each other; so that the original mass gradually decomposes under the influence of various causes. The first step to decay is a process of fermentation, which is more or less rapid in proportion as heat and moisture are more or less present. In the absence of damp air, even the vegetable mass will of itself supply moisture; for, according to Count Rumford, the best-seasoned timber retains one-fourth of its weight of water. A certain extent of moisture is essential to vegetable fermentation; but a complete saturation appears inimical to it. A temperature not so low as to produce freezing, nor so high as to produce rapid evaporation, is also favourable to it. The humidity of the air in ships, and in houses built on clay or in moist situations, and the difficulty of obtaining a free circulation of air, contribute greatly to this fermentative process.

The chemical constitution of the vegetable kingdom yields to analysis only three or four ultimate elements, viz., oxygen, hydrogen, and carbon, and sometimes nitrogen. The most active agent in the process of decomposition is the oxygen contained in the dead plant, whether such decomposition proceed under the rapid influence of fermentation, or be produced more slowly by the operation of the law which renders decay the necessary consequence of organization. As soon as the tree is felled, the oxygen begins to be liberated and to act upon the woody fibre, combining with its carbon, and producing carbonic acid gas. The tenacity of the several parts is thus gradually destroyed. After timber is felled, and during the process of seasoning, a gradual diminution of strength may be remarked. The effect, however, of seasoning is to deprive the wood of superabundant moisture, and of those vegetable juices which would otherwise induce a rapid decomposition.

In addition to the natural decay of timber, the decomposition is often accompanied by the apparently spontaneous vegetation of parasitical fungi, inducing a species of decay to which the term “dry rot” is applied, probably in consequence of the attendant phenomena; the wood being converted into a _dry_ friable mass, destitute of fibrous tenacity. It is uncertain whether the seeds of these fungi exist in a dormant state in the juices of the timber, and wait only until the first stages of decomposition furnish them with a nidus favourable to their growth; or whether they float in the atmosphere and settle in places favourable to their vegetation. It is found, however, that badly-seasoned timber is peculiarly subject to this species of decay; and hereby the former of the two suppositions is favoured.

From the moment when timber is felled, the process of decay commences, and although so slowly in many cases that we are not conscious of it, yet there is a limit to the existence of the most durable articles of wood, however carefully preserved. Dryness, cleanliness, a free circulation of air, or the entire exclusion of it, are among the best checks to vegetable decomposition: while damp accumulations, and a vitiated atmosphere, rapidly induce it.

Unseasoned timber should never be used in carpentry, and the best-seasoned timber should be used only in a dry state. Diseased and decayed portions of the wood should be cut out, together with the sap-wood, which, being more soft and porous than the spine, is more liable to fermentation.

The iron fastenings used about timber frequently cause its premature decay. Iron, under the influence of moisture becomes rusty, that is, oxygen, either from the air or from the wood itself, unites with the metal, forming an oxide, which, in its turn acts upon the woody fibre, and gradually destroys its tenacity. The iron is further subject to attack from the acid juices of the wood; this effect, however, varies in different woods. Oak contains a smaller proportion of oily or resinous particles than many other kinds of wood; and, in addition to the usual vegetable acid common to most woods, oak contains an acid peculiar to itself, called _gallic_ acid. In teak, on the contrary, the quantity of acid is not only smaller, but the resinous particles are very abundant, and these form a sort of protecting covering to the iron fastenings. Maconochie states, on the authority of the shipping built in India and used in the India trade, that the average duration of an iron-fastened teak ship is thirty years; and that it is a misapplication of expense to use copper fastenings with teak, as the additional advantage gained is not at all commensurate with the additional expense. But it is different with oak; the action of oak on copper is by no means so destructive as on iron, and the reaction of the metal on the wood is not so destructive.

The methods which have been from time to time adopted for the preservation of timber are so numerous, that a slight sketch of them would probably fill a good-sized volume. We will name a few of the most successful, and terminate this notice with a description of the method now in practice.

Maconochie recommends all the iron fastenings to be provided with a protecting paint, and to impregnate the timber with some oily preparation, which he proposes to effect thus: the wood is to be placed in a steam-tight chamber, and subjected to the action of steam, by which the air will be expelled from the timber. Then by condensing the steam, and repeating the process until all the elastic fluids are withdrawn from the wood, and its juices converted into vapour, the wood becomes freed from them, and if plunged into oil, and subjected to atmospheric pressure, all the internal cavities of the wood will be filled with oil. In this way, Maconochie had in daily use a steam-chamber capable of containing twenty or thirty planks of timber forty feet long, in which, while the planks were steaming, to render them flexible, they were impregnated with teak oil. He says the oil may easily be procured from the chips and saw-dust used for the fuel of the steam-boilers; for it has been ascertained that Malabar teak contains such a quantity of oleaginous (oily) or terebinthinous (turpentine) matter, that the chips from the timber and planks of a ship built of it will yield, by a proper process, a sufficient quantity of tar for all its own purposes, including the rigging; and that, although oak timber does not contain so much of these substances, the chips of the fir alone consumed in the Royal Navy, would be more than sufficient to supply tar to saturate the oak.

There have been many other proposals to saturate timber with different substances; the most successful of which, up to the process of Mr. Kyan, was that of M. Pallas, whose plan was to saturate the timber in a solution of sulphate of iron, and then precipitate the salt by means of lime-water. About the year 1822, Mr. Bill produced samples of timber impregnated throughout with a substance resembling asphaltum. These samples were subjected to a trial of five years in the dry-rot pit at Woolwich, and withstood the fungus-rot perfectly. Sir John Barrow recommends kreosote, which he says, “in a vaporous form, penetrates every part of the largest logs, and renders the wood almost as hard as iron--so hard as not easily to be worked.”

Mr. Kyan’s plan, now so universally adopted, is to soak the timber in a solution of bichloride of mercury, commonly called corrosive sublimate.

“Aware of the established affinity of corrosive sublimate for albumen, Mr. Kyan applied that substance to solutions of vegetable matter, both acetous and saccharine, on which he was then operating, and in which albumen was a constituent, with a view to preserve them in a quiescent and incorruptible state; and obtaining a confirmation of his opinions by the fact, that during a period of three years, the acetous solution, openly exposed to atmospheric air, had not become putrid, nor had the saccharine decoction yielded to the vinous or acetous stages of fermentation, but were in a high state of preservation, he concluded that corrosive sublimate, by combination with albumen, was a protection against the natural changes of vegetable matter. He conceived, therefore, if albumen made a part of wood, the latter would be protected by converting that albumen into a compound of protochloride of mercury and albumen; and he proceeded to immerse pieces of wood in this solution, and obtained the same result as that which he had ascertained with regard to the vegetable decoctions.”--BIRKBECK.

It having been found that the precipitate caused by the Kyanization was soluble in salt water, Sir William Burnett has lately substituted chloride of zinc for corrosive sublimate, and the resulting compound which this forms with the albuminous portion of the wood, effectually resists the action of salt water.

Soluble Glass.

A remarkable method of preserving wood-work, and rendering it fire-proof, was invented some years ago by M. Fuchs, in consequence of his discovery of a kind of glass which could be prepared and kept in a liquid state, and hardened only on being exposed in a thin layer to the air.

Soluble glass is a union of silica and an alkali, which has, in addition to some of the properties of common glass, the property of dissolving in boiling water. The preparation of soluble glass does not greatly differ in its early stages from that of common glass, an account of the manufacture of which will be found in the eighth chapter.

When sand and carbonate of potash are heated together, the carbonic acid is not entirely driven off, unless the sand be in excess, but the whole of the gas may be expelled by the addition of powdered charcoal to the mixture.

Carbonate of potash and pure sand being taken in the proportion of two to three, four parts of charcoal are added to every ten parts of potash and fifteen of sand. The charcoal accelerates the fusion of the glass, and separates from it all the carbonic acid, a small quantity of which would otherwise remain, and exert an injurious effect. In other respects the same precautions that are employed in the manufacture of common glass are to be observed. The materials must first be well mixed, then fritted, and finally melted at a high heat, until a liquid and homogeneous mass be obtained. This is removed by means of an iron ladle, and the glass pot filled with fresh frit.

The crude glass thus obtained is usually full of bubbles: it is as hard as common glass: it is of a blackish gray, and more or less transparent at the edges. Sometimes it has a whitish colour, and at others is yellowish or reddish, indicating thereby that the quantity of charcoal has been too small. Exposed to the air for several weeks, it undergoes slight changes, which tend rather to improve than injure its qualities. It attracts a little moisture from the air, which slowly penetrates its mass without changing its aggregation or appearance, except that it cracks, and a slight efflorescence appears at its surface. If after this it be exposed to heat, it swells up, owing to the escape of the moisture it has absorbed.

In order to prepare the glass for solution in water it must be reduced to powder by stampers. One part of the glass requires from four to five of water for its solution. The water is first boiled in an open vessel, the powdered glass is added gradually, and is continually stirred, to prevent its adhesion to the vessel. The boiling must be continued for three or four hours, until no more glass is dissolved. If the boiling be checked before the liquor has thus attained the proper degree of concentration, carbonic acid will be absorbed by the potash from the air, and produce an injurious effect. When the solution has acquired the consistence of syrup, and a density of 1·24, it is fit for use. It is then allowed to repose, in order that the insoluble parts may be deposited: while it is cooling a film forms on the surface, which after some time disappears, or may be dissolved by depressing it in the liquor.

Soluble glass being employed only in the liquid state, it is preserved for use in solution. No particular care is necessary to preserve the liquid, as, even after a long space of time, it undergoes no perceptible change, if the solution have been properly prepared. The only precaution is not to allow too free an access of air to it.

Soluble glass may be prepared by using carbonate of soda, instead of that of potash. This glass has the same properties as the other, but is more valuable in its applications. The solutions of these two kinds of glass may be mixed in any proportion, and the mixture is sometimes more useful than either of the solutions separately.

The solution of soluble glass is viscid, and when concentrated becomes turbid or opalescent. The solution unites with water in all proportions. At a density of 1·28 it contains nearly 28 per cent. of glass, and if the concentration be carried beyond this point, it becomes so viscid that it may be drawn out in threads like molten glass. When the solution is applied to other bodies, it dries rapidly in the air, and forms a coat like a varnish; a property which leads us to notice some of the numerous and varied applications of this curious preparation.

It is well known that all sorts of vegetable matter, such as wood, cotton, hemp, linen, paper, &c., are combustible, but in order to burn them, two conditions are necessary,--an elevated temperature, and free access of air to supply the oxygen necessary to their conversion into water and carbonic acid. When once inflamed their own combustion supplies the heat necessary to the chemical action, provided they be in contact with the air. If deprived of such contact, and made red-hot, they will yield inflammable volatile products, but the residual carbon will not burn, because deprived of air; and thus the combustion will cease of itself. Such is the property of all the fixed fusible salts, if they be composed of substances incapable of yielding their oxygen at a low red heat, either to carbon or hydrogen. Such salts melt as the vegetable matter becomes healed: they form upon it a coating impermeable by air, and either prevent or limit the combustion. The phosphate and borate of ammonia have such a character, but they are so readily soluble in cold water as to be liable to objections which are not found in soluble glass. This last-named substance forms a solid and durable coating, which suffers no change by exposure to the air (since soluble glass possesses the valuable properly of being almost entirely unaffected by cold water): it does not involve any great expense, and is easy of application. But in order that it may not fail, particular care must be taken, both in preparing and employing it. To cover wood and other bodies with it the solution must be made of a pure glass, otherwise it would effloresce and fall off. But still a slight degree of impurity is not injurious, although after a few days a slight efflorescence will appear: this may be washed off by water, and will not occur a second time. When a durable coating is to be applied to wood, the first solution must not be too strong, for if it be it will not be absorbed: it will not displace the air from the pores, and consequently will not adhere strongly. A more concentrated solution may be employed for the after-coats, but each coat must be dry before another is applied, and the drying, in the most favourable weather, will occupy at least twenty-four hours. When the glass is made with potash the coating is liable to crack: this defect does not apply to glass made with soda.

Although soluble glass is of itself a good preservative from fire, yet it fulfils the object better when mixed with incombustible powders, such as those procured from clay, whiting, calcined bones, powdered glass, &c. In applying soluble glass to the wood-work of a public building at Munich, ten per cent. of yellow clay or yellow earth was added. After six months the coating had suffered but little change: it was damaged only in a few places, where it had need of some repair. This arose from the very short time allowed for the preparation and application of the glass.

On Veneering.

In our notice of the interior fittings of houses of the better class, it was stated that the process of veneering is sometimes adopted for wainscoting. This process is most generally used for articles of furniture, and deserves to be noticed on account of its ingenuity.

The employment of wood for articles of domestic use or ornament, gives rise to many departments of mechanical labour, according to the manner in which the grain of the wood is to be made conspicuous or visible. In the antique pieces of furniture still existing in old mansions, the wood employed, such as oak, walnut-wood, mahogany, &c., was always solid; but in modern times, the desire of making a respectable appearance, at as small an outlay as possible, has led to the method of _veneering_,--that is, making some article of furniture of some cheap wood,--such as deal,--and then covering it with thin leaves or sheets of some more expensive and beautiful wood, such as rose-wood, maple, satin-wood, zebra-wood, pollard oak, &c. So very prevalent has this custom become, that almost every house now contains some article of domestic furniture, whose surface is covered with a kind of wood more valuable than that of which the bulk of the article is made.

It must be obvious, that the mode of procuring or preparing the thin leaves of veneer calls for great care and nicety, since they are seldom thicker than a shilling. When the method of veneering was first introduced, the sawing was effected by hand, in a manner more rude than the necessities of the case warranted; but when circular saws became introduced, they were found very efficacious for cutting veneers. Mr. Brunel, in 1805, took out a patent for improvements in the machinery for sawing timber, in which he employed a large circular saw, composed of several pieces fitted together, and placed in a frame at such an elevation that the lower edge was a little below the lower side of the timber. The timber was placed in a carriage, and moved towards the saw by a rack.

In such a manner as this veneers are now cut from the timber in this country. But it is stated that the Russians have devised a very curious and effective method of cutting veneers, without the use of a saw, and without making any waste of material. It is a _planing_ machine, the action of which is so accurate, that veneers thin enough for the covering of books, and for lithographic and other engravings, have been produced; thus serving the place of paper. The operation is begun by placing the timber from which the leaf is to be cut upon a square axle, where it is revolved, and made circular by a turner’s gouge. The blade of a plane of highly-tempered steel, and rather longer than the cylinder of wood, is fixed at the extremity of a frame six or seven feet in length, in such a manner as to exert a constant pressure upon the cylinder, and pare off a sheet of equable thickness, which folds upon another cylinder like a roll of linen. The frame to which the blade is attached is moveable at its lower extremity, and by the action of a weight it depresses in proportion as the mass diminishes in substance. That this depression may be progressive and perfectly regular, the inventor has appended a regulator to the machine consisting of a flat brass plate, preserved in an inclined direction, upon which the frame descends as the regulator itself is advanced. The motion is communicated to the cylinder of wood by several cog-wheels, which are turned by a crank. One hundred feet in length of veneering may be cut by this machine in the space of three minutes.

When veneers are produced by the action of circular saws, as is now almost universally the case in England, it is evident that both surfaces must be rough, from the marks of the serrated edge of the cutting instrument; and it is in this rough state that they are purchased by cabinet-makers or others who employ them in veneering articles of furniture. The operations which are then to be performed are, to bring the surface of the veneer to a tolerable level, to fix the veneer to the article of furniture, and to clean and polish it when so fixed.

Supposing the top of a sideboard to be the article which is to be veneered. The workman cuts out a piece of veneer, a little larger than is actually required, to allow for waste; and then lays it flat on his work-bench. With a veneering plane--which is a small-sized plane, having an iron jagged with notches like the teeth of a very fine saw--he works steadily over the whole surface of the veneer, carrying the plane in the direction of the grain of the wood. The action of this plane-iron removes all the saw marks, which were irregular in their course, and gives instead of them a series of regular parallel channels from end to end of the piece of veneer; these channels are but small in depth, and their object is to retain the glue which is afterwards used in the process of veneering.

The surface of the deal or other wood on which the veneer is to be laid, is in like manner planed with these parallel indentations; and then the process of veneering proceeds. The wood, having been well warmed before a fire, is coated with warm melted glue; and the piece of veneer is laid down flat on the veneered surface, and rubbed backwards and forwards, in order that the glue which is between the veneer and the under-wood may be pressed into all the little grooves produced by the plane. When the glue begins to get cool, the veneer can no longer be pressed to and fro, and is then left. This glueing has the general effect of making the veneer adhere to the foundation beneath; but there are parts where, from the accumulation of too much glue in one part, or from the presence of air which had not been expelled by the pressure of the hands, the veneer rises up as a kind of blister, convex on the upper surface. The workman employs a veneering hammer to level these protuberances. This veneering hammer is a piece of wood three or four inches long, and an inch in thickness, having a straight strip of iron plate fixed to one edge. The workman, placing the iron edge down upon the veneer, presses on the block of wood with his hand, and works all over the surface of the veneer, expressing all the superfluous glue from the parts which had formed the protuberances. As this redundant glue must have some place from whence to escape, the workman begins rubbing at the centre, and thence proceeds towards the edge, at which the glue finally exudes. There is a curious plan adopted for ascertaining whether there are any parts, imperceptible to the eye, where the veneer does not adhere closely to the foundation--viz., by sound. The workman strikes the veneer all over with a wooden or other hammer; and if the sound be distinct and solid, he knows that the proper degree of adhesion has taken place; but if the sound be hollow and dull, it indicates the existence of a vacant space between the veneer and the foundation; and a greater degree of rubbing or pressing is consequently necessary. If the surface of the piece of veneer be of large dimensions, two workmen are required to level all parts of the veneer before the glue gets cold and loses its fluidity.

But this operation--however good the glue may be, or however well the veneer may be pressed down--is not sufficient to cause the veneer to adhere permanently to the foundation, especially at the edges, where the air is liable to enter, and to cause the veneer to rise. To prevent this inconvenience, the veneer, at and near the edges, is kept down, either by the pressure of heavy weights, or, still better, by the action of screw-presses. These screw-presses consist of two pieces of wood or clamps, which are brought to any degree of closeness by means of two wooden screws, each screw passing through holes in both clamps, the handles of the two screws being, respectively to each other, outside the opposite clamps. The clamps are opened, by means of the screws, to such a width as to admit the edge of the veneered wood between them; and the screws are then worked up till the clamps grasp the wood tightly, where they remain till the glue is quite cold, and the veneer closely adhering to the foundation.

But even all this care is not in every case sufficient to produce a firm adhesion of the veneer to the foundation. It frequently happens that, when the hardened veneered surface is tried with the hammer, a hollow sound indicates that there is yet a place where the veneer has a vacancy beneath it. In such a case, the only remedy is one of a curious kind--viz., to lay a hot iron on the defective part of the veneer, by which the glue beneath is remelted. A small part of the veneer, reaching from the defective part to the edge, is also similarly heated, and the glue beneath remelted. Then, by means of the veneering hammer, the superfluous glue which had caused the defect is squeezed out, and pressed to the edges of the veneer through the kind of channel which had been prepared for it by the heated iron.

Where the surface of the wood to be veneered is more or less cylindrical, such as a pillar, the front of a drawer, &c., the piece of veneer has a curvature given to it, corresponding in some degree to that of the surface on which it is laid, by the action of hot water, before the glueing is effected. By sponging one side of the veneer with hot water, it causes that side to swell, while the other side remains dry; the consequence of which is, that the wetted surface rises into a convex form, leaving the other side hollow or concave:--this is, in fact, an instance of _warping_, where a thin piece of wood is either unequally heated or damped on opposite sides. The hollow side is then laid on the glued foundation.

When the veneered surface is dry, its edges are trimmed, and its surface scraped and sand-papered, preparatory to the finishing processes which the piece of furniture is to undergo.

Manufacture of Glue.

The preparation of this useful article forms a curious and important branch of national industry. The chief use of glue is for binding or cementing pieces of wood together, as practised by the carpenter and cabinet-maker, in which trades very large quantities are constantly employed.

Glue (which is nothing more than gelatine in a dry state) is obtained from the hides, hoofs, and horns of animals; the refuse of the leather-dresser, and the offal of the slaughter-house; ears of oxen, calves, sheep; parings of parchment, old gloves; and, in short, animal skin and (by a late improvement) bones, are all employed for making glue.

The first process in this manufacture is to free the materials from dirt, blood, and other matters which do not afford glue. For this purpose they are steeped in lime and water, and then placed in baskets, and rinsed by the action of a stream of water. They are then removed to a sloping surface, and allowed to drain, and whatever lime remains is deprived of its caustic property by the reabsorption of carbonic acid from the atmosphere, since the presence of lime would prove injurious in the subsequent processes.

The gelatine is removed from the animal matter by boiling. This process is effected in a somewhat shallow boiler, which is provided with a false bottom, pierced with holes, and elevated a few inches, thus serving as a support to the animal matter, and preventing it from burning by the heated bottom of the boiler. The boiler is filled about two-thirds with soft water, and then the animal substances are added: these are piled up above the brim of the boiler, because soon after boiling commences, they sink down below the level of the liquid. The contents of the boiler are occasionally stirred up and pressed down, while a steady boiling is maintained throughout this part of the process.

As the boiling proceeds, small portions of the gelatine are drawn off into egg-shells, when, in the course of a few minutes, if the liquid gelatine becomes, by exposure to the cool air, a clear mass of jelly, the boiling process is complete,--the fire is smothered up, and the contents of the boiler left to settle for ten or twenty minutes. The stop-cock is then turned, and the gelatine flows into a deep vessel, kept hot by being surrounded with hot water, and thus it remains for several hours, during which time it deposits any solid impurities. It is then drawn off into congealing boxes, and prepared as we shall soon explain.

The undissolved matter in the boiler is treated with boiling water a second, and even a third time, and the above process continued until nothing more can be extracted. The subsequent solutions are often too weak to be made into glue, but they are economically used with fresh portions of animal matter.

A clear idea may be formed of this part of the manufacture by the annexed illustration, which represents a section of three vessels, on different levels. The uppermost vessel, which is heated by the waste heat of the chimney, supplies warm water to the animal matter contained in the second vessel: the third vessel receives the liquid gelatine, and retains it in a fluid state, while the solid impurities are being deposited.

The gelatine is drawn off from this third vessel into buckets, and conveyed to the congealing boxes. These boxes are of deal, of a square form, but somewhat narrower at bottom than at top. The liquid glue is poured through funnels, provided with filter-cloths, into the boxes until they are entirely filled. This process is conducted in a very cool and dry apartment, paved with stone and kept very clean, so that any glue which may be spilt may be recovered. In twelve or eighteen hours the liquid glue becomes sufficiently firm for the next process, which is performed in an upper story, furnished with ventilating windows, so as to admit air on all sides. The boxes are inverted on a moistened table, so that the cake of jelly may not adhere to it: this cake is cut into horizontal layers, by means of a brass wire, stretched in a frame, and is guided by rulers, so disposed as to regulate the thickness of the cake of glue. The slices thus formed are carefully lifted off, and placed on nets stretched in wooden frames. As these frames are filled they are placed over each other, with an interval of about three inches between every two frames, so that the air may have free access. Each frame is so arranged as to slide in and out like a drawer, to allow the cakes to be turned, which is done two or three times every day.

An experienced writer on manufactures thus observes, concerning this part of the process:--“The drying of the glue is the most precarious part of the manufacture. The least disturbance of the weather may injure the glue during the two or three first days of its exposure. Should the temperature of the air rise considerably, the gelatine may turn so soft as to become unshapely, and even to run through the meshes upon the pieces below, or it may get attached to the strings and surround them, so as not to be separable without plunging the net into boiling water. If frost supervene, the water may freeze, and form numerous cracks in the cakes. Such pieces must immediately be remelted and reformed. A slight fog even produces upon glue newly exposed a serious deterioration, the damp condensed upon its surface occasioning a general mouldiness. A thunder-storm sometimes destroys the coagulating power in the whole laminæ at once, or causes the glue to _turn_ on the nets, in the language of the manufacturer. A wind too dry or too hot may cause it to dry so quickly as to prevent it from contracting to its proper size, without numerous cracks and fissures. In this predicament the closing of all the flaps of the windows is the only means of abating the mischief. On these accounts it is of importance to select the most temperate season of the year, such as spring and autumn, for the glue manufacture.”

When the glue is properly dried a gloss is imparted to each cake, by dipping it in hot water, and passing over it a brush, also wetted with hot water. The cakes are then placed on a hurdle, dried in the stove-room, or in the open air, if the weather be sufficiently dry and warm. It is then packed in casks for sale.

It has been found by experiment that when two cylinders of dry ash, one inch and a half in diameter, were glued together, and after twenty-four hours torn asunder, a force of 1260 pounds was required to produce the separation, thus making the force of adhesion equal to 715 pounds per square inch. Another experiment made the force of adhesion to equal 4000 pounds on the square inch.

The House-Decorator of Italy.

In an interesting notice, by Mr. Wilson, of the present state of the arts in Italy, read before the Society of Arts, in Scotland, in November, 1840, a few details are given of the skill with which the house-builder converts the commonest materials into tasteful decorations. The following is an abstract of that part of the notice which relates to the subject of the present volume:--

Notwithstanding the comparatively small employment afforded to Italian architects in the present day, yet there can be no question as to the skill displayed in erecting their designs. The masonry is excellent, and the ancient Roman brick-work is rivalled by that of the present generation; houses are built of brick, in which all the exterior decorations are moulded in that material as perfectly as if executed in stone. The skill with which the Italian workmen build in brick, may be exemplified by the Florentine practice of arching over rooms without centering of any description. Two thin moulds of board, the shape of the intended arch, alone are used: these are placed at each end of the apartment which it is intended to cover in, and pieces of string are stretched from the one to the other, guiding the workman as he advances in the formation of his arch, which he builds, uniting the bricks by their thin edges (greatly thinner than those we use), and trusting entirely to the tenacity and quick-setting of the cement.

Plastering is also carried to a perfection in Italy, of which we have very little idea in this country; rooms are so exquisitely finished, that no additional work in the shape of house-painting is required; but the polish of the plaster, and its evenness of tint, are such as to rival those of the finest porcelain. Sometimes the plaster is fluted, or various designs are executed in _intaglio_ upon it, in the most beautiful manner. Scagliola, a very fine preparation from gypsum, is the material chiefly used. An instance of the cheap rate at which this work is done, is afforded in the new ball-room in the Palazzo Pitti grand-ducal residence at Florence, which, including mouldings, figures, bas-reliefs, and ornaments, was executed at a cost of two crowns for every four square feet.

A most beautiful art among the Italians, and one which might be advantageously introduced into this country, is that of making what are termed Venetian pavements. This method of finishing the floors of rooms is conducted in the following manner. In the first place a foundation is made of lime mixed with pozzolana, and small pieces of broken stone; this is, in fact, a sort of concrete, which must be well beaten and levelled. When this is perfectly dry, a fine paste, as it is termed by the Italians, must be made of lime, pozzolana, and sand; a yellow sand is used which tinges the mixture; this is carefully spread to a depth of one or two inches, according to circumstances. Over this is laid a layer of irregularly broken minute pieces of marble of different colours, and if it is wished these can be arranged in patterns. After the paste is completely covered with pieces of marble, men proceed to beat the floor with large and heavy tools made for the purpose; when the whole has been beaten into a compact mass, and the paste appears above the pieces of marble, it is left to harden. It is then rubbed smooth with fine-grained stones, and is finally brought to a high polish with emery powder, marble dust, and lastly, with boiled oil rubbed on with flannel. This makes a durable and very beautiful floor, which in this country would be well adapted for halls, conservatories, and other buildings.

The carpentry of the Italians, as observable in ordinary houses, displays little skill and indifferent workmanship, but in the roofs and floors of important buildings, they satisfactorily prove their knowledge of scientific principles, and several of their designs are well known to British architects.

With regard to the working of iron, in comparison with our system, the Italian is primitive indeed; yet at times he can and does produce very good specimens of workmanship, but at a heavy cost; consequently they are generally content with very ordinary productions. A manufactory of wire, and of driving and screw nails, by means of machinery, now occupies the villa of Mecænas at Tivoli; the articles produced are very well made. Copper is extensively used in Italy, and there are productive mines in the _Maremma Toscana_. The workmanship of articles made of this metal is respectable; various utensils are made of brass in a neat and satisfactory manner, but in the interior finishing of houses, if much nicety is required, articles of foreign manufacture are used.

House-painters may be mentioned in the last place, and these display much taste and skill; and there is a class of them who greatly excel those in this country, having more the feeling and taste of artists. Surrounded by the finest models in this art, the Italian decorator enjoys every advantage in its study, and he inherits besides from the best periods of art, or rather from antiquity, taste, and a good system of workmanship. He is not a mere machine, employed in the use of the moulds, stamps, and other mechanical contrivances, which too often keep the decorative arts within such narrow limits.

Fresco Painting.

The proposed introduction of Fresco Painting into our public buildings will, it is hoped and expected, have the effect of employing the artist in fresco upon the walls of our dwelling-houses. Already have a few of the mansions of our nobility been thus decorated, and in anticipation of its general introduction it may not be out of character with this little work to describe the process in detail.

Respecting the origin of the term fresco there are two opinions; according to some the term is said to have been adopted because the practice of it is used in the open air. Thus in the Italian language, _andare al fresco_ signifies “to take the air;” or “to walk abroad in the air;” but a more probable explanation is to be found in another meaning of the word fresco, viz., “new,” or “fresh,” as applied to the state of the plaster in which it is wrought. The artist traces his design, colours it, and completely finishes in one day so much of his picture as will occupy the wet plaster ground that has been prepared for him, so that when the ground is dry, he may not retouch any part of his work. This is the characteristic distinction of painting in fresco--a method by which the painting is incorporated with the mortar, and drying along with it becomes extremely durable, and brightens in its tones and colours as it dries.

It will therefore be readily conceived that the artist in fresco has to encounter difficulties of no ordinary kind; a few of them are thus noticed by a writer in REES’S _Cyclopædia_:--“From the necessity there is in the progress of this style of art, that it should be executed with rapidity, and from the impossibility of retouching it without injuring the purity of the work, the artist, unless he be endowed with very extraordinary powers of imagination and execution indeed, is obliged to prepare a finished sketch of the subject, wrought to its proper hue and tone of colour, and so well digested, that there may be no necessity for making any essential alterations in the design. This, which is a very useful mode of proceeding in all fine works of painting, is absolutely indispensable in fresco, to those who are not determined to give the rein to their ideas, and leave as perfect whatever may first present itself. There is no beginning in this, by drawing in the whole of the parts at one time, and correcting them at leisure, as is the custom with oil-painters, who may therefore proceed to work without a sketch; here all that is begun in the morning must be completed in the evening; and that almost without cessation of labour, while the plaster is wet; and not only completed in form, but also, a difficult, nay, almost impossible task, without a well-prepared sketch, must be performed, viz., the part done in this short time must have so perfect an accordance with what follows, or has preceded, of the work, that when the whole is finished, it may appear as if it had been executed at once, or in the usual mode, with sufficient time to harmonize the various forms and tones of colour. Instead of proceeding by slow degrees to illuminate the objects, and increase the vividness of the colours, in a manner somewhat similar to the progress of nature in the rising day, till at last it shines with all its intended effect, which is the course of painting in oil, the artist working in fresco must at once rush into broad daylight, at once give all the force in light, and shade, and colour, which the nature of his subject requires, and this without the assistance (at least in the commencement) of contrast to regulate his eye; so that here, as has been said, a well digested and finished sketch seems indispensably requisite.”

The custom of decorating walls with paintings is very ancient. Those discovered by Belzoni, among the royal tombs of Egypt, prove the existence of the art among the Egyptians many centuries before the Christian era. There is also abundant evidence that it was practised by the Etruscans and Romans. But the more common practice up to the time of Augustus seems to have been to paint the walls of houses of one single colour, and to relieve this with fantastic ornaments. According to Pliny, Augustus was the first to suggest the covering of whole walls with pictures and landscapes. About the same time a painter named Ludius invented that style of decoration, now called _arabesque_ or _grotesque_, many beautiful examples of which have been discovered at Pompeii and other places. The invention of the Arabesque style, as its name implies, has been improperly claimed for the Arabians of Spain; whose religion forbidding the representation of animals, they employed foliage, stalks, stems, tendrils, flowers, and fruit, in a variety of forms and combinations, with which they adorned the surfaces of their buildings. Hence the fanciful combinations of natural objects occupying a flat surface came to be called Arabesque, although it differed so much from the Mohammedan compositions as to contain animals real or fabulous. That the term is badly chosen, especially as applied to the fanciful enrichments on the walls of Pompeii, &c., will be seen from the fact that such ornaments were invented and executed long before the sons of Ishmael had learned to draw. The term grotesque is less objectionable: it is derived from the subterranean rooms (grotte) in the baths of Rome, in which those specimens of ancient art were found, from which Raphael derived the plan of the beautiful frescos which adorn the piers and pilasters of the arcaded gallery of the palace of the Vatican, called, in honour of the artist, “Le Logge di Raffaelle.”

The practice of Fresco Painting may be conveniently considered under the following heads:--1. The cartoon. 2. The preparation of the wall. 3. The process of painting. 4. The colours and implements. The methods as adopted by different artists are of course subject to variation; but as general principles are not altered by variations in those details which conduce to the same end, so the following may be taken as an accurate exposition of the practice of the art.