When cornices are to he charged with ornaments, the plasterer leaves certain indentions, or sinkings, in the mould, in which the casts are laid. These ornaments were formerly made by hand, by artists called ornament plasterers ; but now they are east in plaster of Paris, which has almost supe• seded that branch of art ; at least, the few professors of it remain, are limited in their labours to the modelling and forming of moulds to east from. Ornaments, to be cast in plaster of Paris, are previously modelled in clay from the design. When the clay model is finished, and has acquired sonic degree of firmness from the action of the atmosphere, a wooden frame is adapted to it, and after it has been retouched, and finished, the frame is tilled up with melted wax, which, when cool, on the mould being turned upside down, drops off, and presents an exact cameo, or counterpart, of the model, in which the most enriched and curiously wrought mouldings may be east by the common plasterer. These wax models are contrived to cast about a foot in length of the ornament at once ; such lengths being most easily got out from the cameo. The casts are made of the finest and purest plaster of Paris, saturated with water ; the wax mould being oiled previously to its being poured in. When first taken from the mould, the casts, or intaglios, are not very firm ; but after they have been suffered to dry a little, either in the open air or in an oven, they become hard, and are scraped and cleaned up for the workmen.
Friezes and basso-relievos are executed in a similar manner, only the wax mould is so contrived that the cast may have a back ground of plaster, at least half an inch thick : this is cast to the ornament, or figure, so that it strengthens and secures proportions, at the same time that it promotes their general (street.
Nor is the process ditThrent for capitals to columns, except that they require a number of moulds to complete them. To make a good mould, however, requires the utmost skill of the modeller. The Corinthian capital requires a shaft, or bell, to be first made, on which are afterwards to be fixed the foliage and volutes ; all which, as well as the other details, require distinct cameos.
In forming cornices that are to be charged with orna ments, the plasterer takes care to have proper projections in the running mould, so as to leave a groove or indention in the cornice, into which the cast ornament is laid, and secured in its place, by spreading a small quantity of liquid plaster of Paris on its back. Friezes, likewise, are prepared for in the cornice in a similar manner, by leaving a projec tion in the running mould, at the part where they are intended to be inserted. and they are fixed in their places by liquid plaster. Detached ornaments, designed for a ceiling, or other part, where no running mould has been employed, are cast in pieces, corresponding with the design, and fixed upon the ceiling, &c. with white-lead, or the composition known under the name of iron eement.
Good plastering is known by its exquisite appearance, both as to regularity and correctness, and its solid effect having no cracks, nor indications of them, visible.
The makiug and working of stucco has, for a considerable time past, occupied the attention of chemists, physicians, architects, and plasterers ; but the only beneficial result has been a more extensive knowledge of the materials used in it : indeed, our climate, from its great moisture, prevents its being brought to superlative perfection, though, among the various compositions that have been proposed and tried, some are comparatively. excellent. The common stucco now
in use fur external work, is known, among plasterers, by the name of Baileys eompo ; it consists of Thames sand cleanly washed, and ground Dorking lime, mixed dry, in the propor tion of three of the latter to one of the former, which when well incorporated together, should be secured from the air in good tight casks, till the moment it is wanted for use. Walls intended to be covered with this composition, must be first prepared, by raking the mortar from the joints, and picking the bricks, or stones, till the whole wall is properly indented. The part must then be clean brushed of all (lust and other extraneous matter, and well soaked with clean water. The stucco is then to be supersaturated with water, till it bears the appearance and consistence of ordinary whitewash: in which state it is to be rubbed over the wall with a flat brush of hogs' bristles, and then left to become tolerably dry and hard, which is ascertained by its becoming more white and transparent than when at first laid on. This process is called roughing in. Screeds are next to be formed upon the wall, with fresh stucco from the cask, tempered with water to a proper consistency, and spread on the upper part of the wall about eight or nine inches wide, and against the two ends, beginning at the top, and proceeding downwards to the bottom. in this operation, two workmen are required ; one to supply the stucco, the other to use and try the plumb-rule and straight-edge. When these are truly formed, other screeds must be made, vertically, about four or five feet apart, unless apertures in the wall should prevent it, in which case they must be formed as near together as possible. When the screeding is all done, more comp() must he prepared, and in larger quantities than was done for the former process; and, when ready, both the workmen begin to spread it with their trowels over the wall in the space left between each pair of screeds that arc nearest together. When this is done the straight-edge is to be applied across both, and dragged from the top to the bottom, so as to remove whatever super fluous stucco may project above the screeds. Should any hollow places appear, fresh stucco must be applied, and the straight-edge again drawn over the spot, till the compo is brought even to the face of the screeds, and the whole is level with the edge of the rule. The workmen then fill up another interval ; and thus they proceed, till the whole of the wall is covered. The wall is then to be finished, by floating, or hardening the surface, by rubbing it with the common wood float, and sprinkling it with water, an opera tion that is performed, as above directed, for troweled stucco; always remembering to begin the floating on the part first filled up.