MARBLE is polished in different modes, which are jointly dependent on the nature of the marble, and the character of the work; some of the principal methods will be described.

Marble is generally worked by the lapidary after the manner of carnelian, sometimes of alabaster, but he is far less successful in this department of art than the sculptor and marble workers. 1. - Marble Ornaments and small works intended for close inspection, and which require the highest possible finish. - "After the marble is sawn into slab the first operation is to grind it down with a flat coarse sand-stone and water, or with an iron plate, fed with fine sand and water, until all the marks of the saw are perfectly removed; 2ndly, a fine sandstone, (procured from Bilston,) is used with water, until the marks made by the first stone are removed; 3rdly, a finer sandstone which is found near Congleton, is applied to work out the marks of the former; 4thly, pumice-stone with water, and 5thly, snake stone is used, and the last finishes what is called the growiding.

"Next comes the polishing, which is principally performed with rollers of woollen cloth or list made to the size of about three inches diameter. As the 6th process a rubber is charged with flour emery and a moderate degree of moisture; this rubber is worked uniformly over every part, until the marble acquires a kind of greasy polish; 7thly, the work is completed with a similar roll of cloth charged with putty powder and water. Some prefer as the polisher, an old cotton stocking not made into a rubber, and in some few of the more delicate works, crocus is used intermediately between the emery and the putty-powder. It is necessary to wash the marble after each operation, so that not a particle of the previous polishing material may remain, otherwise the work will be scratched."

2. - Marble Works Turned in the Lathe. - "Turned works are polished as above, excepting that for the rolls of cloth are substituted two or three thicknesses of cloth supplied with emery or putty powder, and held upon the work by the hand, which is constantly moved about."

For the above paragraphs, and also for the practical remarks on turning marble, the author is indebted to Mr. Hall of the Marble-works, Derby; and for the subsequent particulars to Mr. Thomas Smith, sculptor, of London.

3. - Statuary and large works in marble, which are dependent on their general design and effect, rather than on elaborate finish, are executed by a different class of artists, and require only part of the above proceses to be resorted to. By Statuaries the marble is rubbed with two qualities of gritstone, the coarse, which is somewhat finer than Bilston, is known as first grit, and the fine as second grit. Thirdly, the work is smoothed with snakestone, after which the white or statuary marble is finished with putty powder and water, on a wooden block covered with thick nap, or felted cloth. {See article Rubber.)

The Irish black marble is by some considered harder than the Derbyshire, and after the snakestone has been used, it is polished with tripoli on felt as above, and finished with putty powder or crocus, but the rubber is then covered with three thicknesses of stout linen.

The finest Welsh black marble is esteemed still harder and blacker than the Irish, and after the snakestone, is polished by laying a thin plate of copper or lead on the wooden rubber, and using therewith tripoli and water, and finally putty powder or crocus on linen as before.

The Irish marble is less brittle than the Welsh, and better suited to carved ornaments. Marble has of late years been sawn, ground, and polished to a very great extent, by means of machinery, much of which took its rise from the comparatively old machinery used for the same purposes in Derbyshire. Sculpture. - The dull parts of sculpture are finished in four different manners, or rather, the complete process of smoothing is discontinued at various stages, so as to form four gradations, denoted by the respective paragraphs.

The marble is First, sometimes left from the long and very slender statuary's chisel, the reverse end of which is formed with a sharp circular edge or ridge, just like a hollow center, in order that the metal hammer, which is of soft iron, tin, or zinc, may be slightly indented by the chisel, so as to avoid its glancing off; the chisel marks leave the surface somewhat rough and matted, intermediate between the granular and crystalline character.

Secondly, For surfaces somewhat smoother, rasps are used to remove the ridges left by the chisel, the rasps leave a striated or lined effect suitable for draperies, and which is made more or less regular according to the uniformity of the strokes, or the reverse.

Thirdly, Files are employed for still smoother surfaces of the same character; and it is to be observed that the files and rasps are generally curved at the ends, to adapt them to the curvilinear forms of the sculpture. See the article on Riflers, in the chapter on Files, vol. 2, page 834.

Fourthly, For the smoothest of the dull or unpolished surfaces, the faint marks left by the file are rubbed out with Trent sand or silver sand and water, applied by means of a stick of deal cut to a point, and rubbed all over the work in little irregular circles, as a child would scribble on a slate, and if the end of the stick is covered with two or three thicknesses of cloth, the marble receives a still rounder or softer effect than from the naked stick, for which the cabbage wood or partridge wood is sometimes used, and the end of the stick is slightly bruised, so that the fibres of the wood may assume the character of the stiff brush, known by artists as a scrub.

Mr. Thomas Smith adds that he has successfully copied the minute roughness or granulation of the skin, by a kind of etching which he was induced to try, by imagining that he could trace such a process to have been used in some of the most perfect of the ancient marbles that had not been exposed to open air. The work having been smoothed with sand as above, he takes a hard stubby brush, and therewith dots the marble with muriatic acid, and which quickly, yet partially, dissolves the surface. The stringency of the acid, which must not be excessive, is tested upon a piece of waste marble: the brush is hastily dipped in the acid, applied to the work, quickly rinsed in water, and then used for removing the acid from the marble. It is obvious the process calls for a certain admixture of dexterity and boldness, and sometimes requires several repetitions, the process occupying only a few minutes each time.

Fifthly, The bright parts of sculpture. Few of the works in sculpture are polished, and such as are, are required in the first instance to pass through the four stages already explained for producing the smooth but dull surface; after which, slender square pieces of the second gritstone and of snakestone are used with water as a pencil, and then fine emery and putty powder on sticks of wood; but the work is exceedingly tedious, and requires very great care, that the artistical character of the work, and any keen edges that may be required are not lost in the polishing. To avoid the tediousness and the risk of deterioration, it is not unusual in carved black marbles, and those of dark colours, after using the snakestone, to coat the work with varnish, by which a gloss is given without attrition. The pillars of the Temple Church, London, which are of Durbec marble, were in like manner French polished, after the manner of furniture, when that building was recently restored.