In the founding of statues, busts, &c. three things in particular require atten tion ; namely, the mould, the wax, and shell or coat, the inner mould or core, so called from being in the middle or heart of the statue. In preparing the core, the moulder is required to give it the attitude and contour of the figure intended to be founded. The use of the core is to support the wax and shell, to lessen the weight, and save the metal. The core is made and raised on an iron grate, sufficiently strong to sustain it ; and it is farther strengthened by bars or ribs of iron. The core is made of strong potter's clay, tempered with water, and mixed up with horse-dung and hair, all kneaded and incorporated together ; with this it is modelled and fashioned previously to the sculptor's laying over it the wax; some moulders use plaster of Paris and sifted brick dust, mixed together with water, for their cores. The iron bars which support the core are so adjusted that they can be taken from out of the figure after it is founded, and the holes are restored by solder, &c. ; but it is necessary in full sized figures to leave some of the iron bars affixed to the figure to steady its projecting parts. After the core is finished, and got tolerably firm and dry, the operation of laying on the waxen covering to represent the figure is performed, which must be all done, wrought, and fashioned, by the sculptor himself, and by him adjusted to the core. Some sculptors work the wax separately, and afterwards dispose and arrange it on the ribs of iron, filling up the void spaces in the middle afterwards with liquid plaster and brick-dust, by which plan the core is made as, or in proportion to, the sculptor's progress in working the wax model. Care must be taken, however, in modelling the wax in both cases, to make it of an uniform substance, in order to the metal being so in the work, of which the wax is its previous representative. When the waxen model is finished to the core, or adapted and filled afterwards, small tubes of wax are fixed perpendicularly to it from top to bottom, to serve not only as jets to convey the melted metal to all parts of the work, but as vent holes to allow a passage to the air generated by the heated brass in flowing into the mould, and which, if not admitted readily to escape, would occasion so much disorder in it as would much injure the beauty of the work. Sculptors adjust the weight of the metal required in this kind of founding by the wax taken up in the model. One pound of wax so employed will require ten pounds of metal to occupy its space in the cast ing. The work having advanced in progress so far, will now require covering with a shell. This consists of a kind of coat laid over the wax, which, being of a soft nature, easily takes and preserves the impression, which it afterwards communicates to the metal upon its occupying the place of the wax, which is between the shell and core. The shell is composed of clay and white crucible dust, well ground, screened, and mixed up with water to the consistence of paint, like which it is used. The moulder applies it, by laying it over the wax with a camel's hair or other soft pencil, which will require eight or nine times going over, allowing it time to dry between each successive coat. After this coating is firm upon the wax, and which is used only to protect it from those which are to follow, the second part or coating is made up of common earth, mixed with horse dung ; this is spread all over the model, and in such thick ness as to withstand, in some measure, the weight of the metal. To this coating or impression is added a third, composed almost wholly of dung, with a proportion of earth sufficient only to render it a little more tough and firm when used. When this is tolerably dry, the shell is finished by laying on several more coats or impressions of the same composition, made strong and stiff by successive workings with the hand. When this is finished and is deemed adequate to support the heated metal, it is further secured and strengthened by several bands or hoops of iron, bound round it at about six inches from each other, and fastened at bottom to the grate on which the statue stands. Above the head of the statue is made an iron circle, for the purpose also of confining the shell and statue; to this circle the hoops are fastened at top. It may be considered, when the moulding has arrived at this state, to be in a condition to receive the melted metal ; but it is not so exactly, as will soon appear. The mould, as has been before observed, is made upon an iron grate ; under this grate is a furnace and flue, in which, at this period of the work, a moderate fire is to be made, and the aperture of communication therewith stopped up, so as to keep in the heat. As the heat increases and begins to operate upon the mould, preparation must be made to allow of the wax running freely from out of the shell ; for this purpose pipes are contrived at the base of the mould so that it may run gently off and through these pipes. As soon as it is all run off the pipes are nicely stopped up with earth to prevent the air entering them, &c. When this is done the shell is surrounded by any matter that has non-conducting properties—for instance, pieces of brick put round andpiled up of good thickness, secured by earth, will answer the end ; and the whole should be finally coated outside with loam as a further protection to keep in the heat. After the shell is adequately surrounded with materials to keep off the effect of the air, the fire in the furnace is augmented till such time as both the matter surrounding the shell and it also becomes red hot, and which, in ordinary circumstances, will take place in twenty-four hours' time ; the fire is then extinguished, and the whole allowed to cool ; after which, the matter which has been packed round the shell is taken away, and its place occupied with earth moistened and closely pressed to the mould in order to make it more firm and steady. It will, when having advanced so far, be in a state to receive the melted metal, to prepare which for the casting, a furnace is made a few feet above the one employed to heat the mould; it is formed like an oven, having three apertures, one of which is for a vent, the other to admit the fuel, and the last to let the melted metal flow through and out of the furnace. This last aperture should be kept very close whilst the metal is fusing, when it has arrived at that state which is deemed proper for running it into the shell, and which is known by the quick separation and escape of the zinc of the brass. A little tube is laid to convey it into an earthenware basin, which is fixed up over the to of the mould ; into this basin all the large branches from the jets enter, and from which is conveyed the metal into all parts of the mould. The jets are all stopped up with a kind of plugs, which are kept close till the basin which is to supply the metal be full. When the furnace is first opened for this purpose the melted brass gushes forward like a torrent of fire, and is prevented from entering any of the jets by the plugs, till the basin is sufficiently full to be ready to begin with the mould, and which is esteemed so when the brass it contains is adequate to the supply of all the jets at once, upon which occasion the plugs from all of them are withdrawn. The plugs consist of a long iron rod, with a head at one end, capable of filling the whole diameter of each tube. The hole in the furnace in which the melted metal is con tained is opened with a long piece of iron fitted on the end of a pole, to allow of the furnace man keeping at a distance from it, as many accidents occur by the red hot metal coming in contact with the air, particularly if it be damp, in which case the most violent explosions take place. The basin is filled almost
in an instant after the furnace plug is withdrawn, and the metal is then let into the several jets communicating with the model, which, when they have emptied themselves into the shell or mould, the founding is finished in so far as the casting is concerned. The rest of the work is completed by the sculptor, who takes the new brass figure from out of the mould and earth in which it was en compassed, saws off the jets, and repairs and restores the parts where required. His tools for this purpose consist of chisels of various sizes, gravers, punches, files, &c.
In casting colossal statues a somewhat different mode is pursued than the one already described, and this arises wholly from the size, it being found diffi cult to remove the moulds of such colossal works ; to obviate this difficulty, it is worked and prepared upon the spot where it is to be cast. There are two ways of performing this, and some founders prefer the one and some the other. By the first plan, a square hole is dug into the earth somewhat larger than would be required for the mould, and its sides are hemmed up with brick work ; at its bottom is formed a hole, below the one already prepared, as a furnace, which must be built up with brickwork, having an aperture made outwards into another pit prepared near it, from which the fuel is put into the furnace. The top of the furnace in the first hole is covered by a grating of iron, and on this is moulded and placed the case of the statue to be cast, and also its waxen coating ; in doing which the same process is observed by the sculptor as that already described. Near the edge of the large pit in which the model is placed is erected the furnace to melt the metal, and which is similar to the one already described for common figure casting, except being of larger dimensions ; it has, like that, three apertures—one for putting in the wood, another for a vent, and a third to run the metal out at. By the second plan of founding colossal figures, it is thought sufficient to work the model above ground, adopting the same mode with respect to a furnace and grate under neath it ; for whether under ground or above it, to keep in the heat when drying the core and melting the wax, is the end more particularly sought; to do which in the most effectual way four walls of brickwork are built up round the model, in the middle of which is fixed the grate and furnace ; and on one side above is formed the mass of building intended for the furnace, which is to be appropriated to the melting of the metal. When the whole is finished and ready, a fire is made in the fire-place under the core of the model, and kept up so as to produce a moderate heat to dry the core, and also to melt the wax from off it, which runs down by tubes, as has been before remarked, and indeed no difference whatever takes place in such founding, except every thing being upon a larger scale. When the wax is run off and the fire extinguished in the furnace, bricks are filled in at random, either into the hole, if founding under ground, or into the area between the walls, if above ground ; after this is done, the fire in the furnace is again lighted, and up and augmented till such time as both the core and bricks are of a red heat, when the fire is again extinguished, and the whole is left to cool; and when cooled, the bricks are removed, and all is cleared away, and the space again occupied by moistened earth to secure and steady the model. Nothing now remains but running in the metal, which is performed, as has been before described for smaller foundings of statues.
The casting of guns is performed in the manner already described for statues, excepting that no core is required, it being cast solid, and the cavity entirely bored out, during which operation the gun is turned and finished on the outside. (See CANNON, and BORINO MACHINE.) The composition of which cannon is formed in this country is 10 lbs. of tin to 100 lbs. of copper, whereas, in the brass of statues, zinc is employed instead of tin.
Founding in Bronze.—The Egyptian bronze consisted, according to Bessari, of two-thirds brass and one-third copper. Pliny says, that the Grecian bronze was formed by adding one-tenth lead and one-twentieth silver to the two-thirds of brass, and the one-third of copper of the Egyptian bronze; and that this was the proportion afterwards made use of by the Roman statuaries. The modern bronze is commonly made of two-thirds copper, fused with one-third of brass ; and recently, owing to the great demand for ornaments and decorative furniture of this alloy, lead and zinc in small proportions have been added to the copper and brass. These additions, it is said, increase the fusibility of the alloy, and facilitate the process of casting. Bronze casting is employed in forming eques trian statues, colossal and other figures in alto relievo, to adorn public places, its peculiar tint finely contrasting with the stone or marble of architecture, espe cially when the artist displays taste in his design and skill in his execution. The casting in bronze is performed in the following manner : first, the figure or pattern to be cast must have a mould, and this is prepared and laid on a plaster cast, previously wrought and finished by the sculptor. The mould is made of plaster of Paris, moistened with water, to which is added brick-dust in the proportion of one-third of the former to two-thirds of the latter. This is carefully laid on the mould, with strength in proportion to the weight of metal intended to be used in the founding. In its joints should be cut small channels tending upwards and from different parts of the internal hollow, to allow of vent for the air to escape, as the heated metal runs in upon the mould. A thin layer of clay should be spread over the inside of it, and of the thickness which it is intended the bronze should be. Withinside of the clay a filling-up of plaster and brick-dust, in the proportions as before described, will be required to compose the core ; but if the work to be cast be large, before the plaster and brick-dust are poured into the mould to form the core, a skeleton, composed of iron bars, as a support for the figure, should be prepared and fixed; after which the filling up of the core may be proceeded in. When this is done the mould must be opened again, the layer of clay taken out of it, and the core thoroughly dried, and even burned, with a charcoal fire, or with straw ; for if the least damp remain the cast will be blown to pieces when the hot metal comes in contact with it, in running it into the mould, and the workmen employed about the work be maimed or killed by the dispersion of the heated bronze. After the core, &c. has been properly dried and is deemed ready for the work, it should be laid in the mould, and supported in its place by short rods of bronze, which should run through the mould into the core. All being so far advanced, the mould should be clad and bound round with iron, of strength proportionate to the size of the work to be cast ; after which the mould should be laid in a situation for running in the metals, and must be supported for that purpose by bricks, &c. Great care should be taken that every part be perfectly dried before any metal be run into the mould, or, as has been before observed, the most fatal consequences will arise to those who may be about the work. A channel must be made from the furnace in which the melted metal is, in order to its running to the principal jet of the mould, and with a descent to promote its flowing rapidly. The jets, furnace, &c. &c. are all contrived, as has been before described, for casting figures in brass.