For grinding the edges of marble, large slabs are propped upright against some temporary support, and narrow rubbers of stone or iron supplied with sand and water are applied to the edges. Narrow pieces such as shelves are placed edgeways upon flat slabs, and rubbed lengthways by one or two men.
After the smoothing with silver sand, marble works are rubbed with pieces of first and second gritstone, sometimes with pumice-stone, but which is not generally used on account of the expense, and the grounding is completed with pieces of snake-stone, as mentioned on page 1076. The pieces of gritstone and snakestone are not laid flat upon the work, but placed edgeways at an angle of about 50 degrees, and rubbed in the direction of their breadth, much the same as in sharpening a plane iron or chisel. Flat surfaces in marble are lastly polished with the block, or wooden rubber covered with thick felt, described on page 1089, article 3, and shown in fig. 1089. A piece of stone nearly as large as the block is generally placed upon it as a weight, and the block is rubbed backwards and forwards. The proper succession of polishing powders is mentioned at page 1076, under the head Marble, but it should be observed that crocus is only applied upon dark-coloured marbles, as light-coloured or statuary marbles would be stained by the crocus, and for the last finish the London workmen prefer coarse linen rags.
Mouldings in stone and marble, are worked partly by the chipping chisel and partly by grinding. The drawing of the required moulding is first pricked through upon a piece of cardboard, which is then cut out to the counterpart form of the moulding, and if it be small a copy is made in sheet metal, generally zinc is used for the purpose, as it is easily filed, and a tolerably cheap material, these counterparts made in metal for small mouldings are called moulds, those counterparts made in wood for large mouldings are known as templates, but they arc both applied in exactly the same manner.
The outline of the moulding is first scribed from the mould upon the two ends of the block of stone, and if the moulding is deep so that any considerable portions have to be removed, of either a soft stone that is easily sawn, such as Caen stone, or of any valuable marble, such as statuary marble, the large pieces are removed, either with toothed saws or grub-saws, according to the hardness of the material. If however the stone is hard and not of great value, the principal portion is chipped away in large chamfers; lines are then drawn on the face of the work, to denote the several parts of the mouldings, which parts are worked first as square fillets and small chamfers. The contour of the moulding is then formed with small straight and round-ended chipping chisels, under the guidance of the mould, and the lines on the ends of the block, the quirks of the beads and similar )arts are cut in with grub-saws of suitable thicknesses.
When the mouldings have been rendered as perfect as admis-ible with the chisels, their surfaces are completed by grinding, which is done with stone or iron rubbers, having concave- and convex edges for the curved parts, and square edges for the fillets and flat surfaces, sand of various degrees of fineness being used, according to the progress of the work.
The square iron rubbers for the fillets and square edges are made of bars of iron about 1 inch deep of various widths and from 1 to 3 feet long according to the length of the work, the bar is thinned and turned up at each end for its attachment to the wooden stock upon which it is mounted as shown in fig. 10.90.
Small rubbers entirely of iron and from 2 to 10 inches long are used for these parts of mouldings which are of frequent occurrence, such as beads and astragals, but for the less frequent parts of mouldings, stone rubbers are principally employed, from motives of economy.
The mouldings are finally smoothed and polished with small slips of gritstone and snake stone, followed by putty powder applied on the ends of soft deal sticks, they are afterwards, clouted up or rubbed with pieces of nearly worn-out felt, removed from the blocks used for polishing flat surfaces, and the last finish is given with linen rags and putty powder.*
* Polished marble that has become soiled is best cleaned with a weak lye made of pearl ash and a little soft soap, and which may also be employed to clean alabaster that is only moderately soiled. This method has the advantage of not removing the polish like the more effectual method described on page 1035 of the Catalogue Article 4.
Muriatic acid is sometimes used for cleaning marble but it is ruinous to delicate poured into the recess, and the pattern is inserted bodily, so soon as the cement is set, the second liner and plaster are removed from the surface, but this time the application of the boiling water is not necessary, as the plaster can be readily detached from the smoothed surface with a chisel applied around the edges. The entire face of the slab is now ground and smoothed to make pattern quite level with the margin, after which any imperfections that may exist in the joinings of the pieces, are corrected with the coloured shell-lac stopping or cement, to be hereafter described, and the work is finally polished as usual.
Inlaid works in coloured marbles such as mosaic and other patterns inserted in a flat surface such as a table top, are combined and ground in the following manner. The marbles are first cut into thin sheets from one-eighth to one-fourth of an inch thick, which are cut into pieces of the required forms and smoothed on the edges by filing and rubbing. Temporary slips are then fixed down to a flat surface, within which the pieces of marble to form the pattern are arranged in their proper situations, face downwards, and pressed tightly together, plaster of Paris is poured over the whole, and a slab of stone, or liner, is laid upon the plaster, which thus cements the whole into one mass exactly the same as the single row of squares for a tesse-lated pavement, previously explained. When the plaster is set, the surface of the inlaid work is ground and smoothed as a runner upon a flat slab, until it presents a level surface.