This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
(1) If the piece to be polished is a plane surface, it is first rubbed by means of another piece of marble, or hard stone, with the intervention of water and two sorts of sand; first with the finest river or drift sand, and then with common house or white sand, which latter leaves the surface sufficiently smooth for the process of gritting. Three sorts of grit stone are employed; first, Newcastle grit; second, a fine grit brought from the neighbourhood of Leeds; and lastly, a still finer, called snake grit, procured at Ayr, in Scotland. These are rubbed successively on the surface with water alone; by these means, the surface is gradually reduced to closeness of texture, fitting it for the process of glazing, which is performed by means of a wooden block having a thick piece of woollen stuff wound tightly round it; the interstices of the fibres of this are filled with prepared putty powder (peroxide of tin), and moistened with water; this being laid on the marble and loaded, it is drawn up and down the marble by means of a handle, being occasionally wetted, until the desired gloss is produced. The polishing of mouldings is done with the same materials, but with rubbers varied in shape according to that of the moulding.
The block is not used in this case; in its stead a piece of linen cloth is folded to make a handful; this also contains the putty powder and water. Sand rubbers employed to polish a slab of large dimensions should never exceed 2/3 of its length, nor 1/3 of its width; but if the piece of marble is small, it may be sanded itself on a larger piece of stone. The grit rubbers are never larger than that they may be easily held in one hand; the largest block is about 14 in. in length and 4 1/2 in. in breadth.
(2) Polishing includes 5 operations. Smoothing the roughness left by the burin is done by rubbing the marble with a piece of moist sandstone; for mouldings, either wooden or iron mullers are used, crushed and wet sandstone, or sand, more or less fine according to the degree of polish required, being thrown under them. The second process is continued rubbing with pieces of pottery without enamel, which have only been baked once, also wet. If a brilliant polish is desired, Gothland stone instead of pottery is used, and potters' clay or fullers' earth is placed beneath the muller. This operation is performed upon granites and porphyry with emery and a leaden muller, the upper part of which is incrusted with the mixture until reduced by friction to clay or an impalpable powder. As the polish depends almost entirely on these two operations, care must be taken that they are performed with a regular and steady movement. When the marble has received the first polish, the flaws, cavities, and soft spots are sought out and filled with mastic of a suitable colour.
This mastic is usually composed of a mixture of yellow wax, rosin, and Burgundy pitch, mixed with a little sulphur and plaster passed through a fine sieve, which gives it the consistency of a thick paste; to colour this paste to a tone analogous to the ground tints or natural cement of the material upon which it is placed, lampblack and rouge, with a little of the prevailing colour of the material, are added. For green or red marbles, this mastic is sometimes made of lac, mixed with Spanish sealing-wax of the colour of the marble; it is applied hot with pincers, and these parts are polished with the rest. Sometimes crushed fragments of the marble worked are introduced into this cement; but for fine marbles, the same colours are employed which are used in painting, and which will produce the same tone as the ground; the lac is added to give it body and brilliancy. The third operation of polishing consists in rubbing it again with hard pumice, under which water is constantly poured, unmixed with sand. For the fourth process, called softening the ground, lead filings are mixed with the emery mud produced by the polishing of mirrors or the working of precious stones, and the marble is rubbed with a compact linen cushion, well saturated with this mixture; rouge is also used for this polish.
For some outside works, and for hearths and paving tiles, marble workers confine themselves to this polish. When the marbles have holes or grains, a leaden muller is substituted for the linen cushion. In order to give a perfect brilliancy to the polish, the gloss is applied. Well wash the prepared surfaces, and leave them until perfectly dry; then take a linen cushion, moistened only with water, and a little powder of calcined tin of the first quality. After rubbing with this for some time, take another cushion of dry rags, rub with it lightly, brush away any foreign substance which might scratch the marble, and a perfect polish will be obtained. A little alum mixed with the water used penetrates the pores of the marble, and gives it a speedier polish. This polish spots very easily, and is soon tarnished and destroyed by dampness. It is necessary, when purchasing articles of polished marbles, to subject them to the test of water; if there is too much alum, the marble absorbs the water, and a whitish spot is left.
(3) To polish imitation marbles, when you have finished marbling, let the work stand for a day or two; then gently rub it down with the back or smooth side of a sheet of sandpaper; this will take off the knits or bits of skin which may be upon it, without scratching it; now give it 3 coats of the best pale polishing copal varnish, allowing an interval of 2 days after each coat. Let this stand for 3 weeks; then cut it down with ground pumice and water, using a piece of wash-leather or rag for that purpose When you have got it tolerably smooth and level, wash it well with plenty of clean water, taking particular care to clean off all the pumice; give it 5 coats of varnish. It ought now to stand for 3-6 months before it is polished, for if it is done before it is almost certain to crack. When the varnish is sufficiently hard, cut it down with finely-ground pumice as before; then use rottenstone and olive-oil, with the ball of the hand; then flour and oil; finish off with dry flour. This takes a deal of time to do properly.