Faraday to Henry Hart Milman   30 April 1857¹

<qr>Royal Institution, Albemarle Street, W. | 30th April, 1857.

My dear Dr. Milman,

I wish I could write anything satisfactory, in reply to your note about the marbles in the British Museum. I examined them, in respect of their condition as to dirt, on the 24th instant²; and more particularly a Caryatide, No. 128; the Shaft of a Column, No. 118; and some of the Metopes in the Elgin Gallery. The marbles generally were very dirty; some of them appearing as if dirty from a deposit of dust and soot formed upon them, and some of them, as if stained, dingy, and brown. The surface of the marbles is in general rough, as if corroded; only a very few specimens present the polish of finished marble: many have a dead surface; many are honeycombed, in a fine degree, more or less; or have shivered broken surfaces, calculated to hold dirt mechanically.

I found the body of the marble beneath the surface white. I found very few places where the discolouration seemed to be produced by a stain penetrating the real body of the unchanged or unbroken marble. Almost everywhere it appeared to be due to dirt (arising from dust, smoke, soot, &c.) held, mechanically, by the rough and fissured surface of the stone.

The application of water, applied by a sponge or soft cloth, removed the coarsest dirt, but did not much enlighten the general dark tint. The addition of rubbing, either by the finger, or a cork, or soft brushes, improved the colour, but still left it far below that of a fresh fracture. The use of a fine, gritty powder, with the water and rubbing, though it more quickly removed the upper dirt, left much imbedded in the cellular surface of the marble.

I then applied alkalies, both carbonated and caustic; these quickened the loosening of the surface dirt, and changed the tint of the brown stains a little; but they fell far short of restoring the marble surface to its proper hue and state of cleanliness. I finally used dilute nitric acid, and even this failed; for, though I could have gone on until I had dissolved away the upper marble, and left a pure surface, even these successive applications, made, of course, with care, but each time producing a sensible and even abundant effervescence, and each time dissolving enough marble to neutralize the applied acid, were not sufficient to reach the bottom of the cells and fissures in which dirt had been deposited, so as to dislodge the whole of that dirt from its place.

The examination has made me despair of the possibility of presenting the marbles in the British Museum in that state of purity and whiteness which they originally possessed, or in which, as I am informed, like marbles can be seen in Greece and Italy at the present day. The multitude of people who frequent the galleries, the dust which they raise, the necessary presence of stoves, or other means of warming, which, by producing currents in the air, carry the dust and dirt in it to places of rest, namely, the surfaces of the marbles; and the London atmosphere in which dust, smoke, fumes, are always present, and often water in such proportions as to deposit a dew upon the cold marble, or in the dirt upon the marble, are never-ceasing sources of injury to the state and appearance of these beautiful remains. Still, I think that much improvement would result from a more frequent and very careful washing; and I think that the application of a little carbonated alkali (as soda) with the water, would be better than soap, inasmuch as the last portions of it are more easily removed. It requires much care in washing to secure this result; but whether soap or soda be employed, none should be allowed to remain behind.

Dry brushing or wiping is probably employed in some cases; if so, it should be applied with care, and never, whilst the objects are damp, or from the conditions of the weather likely to be so. In several cases there is the appearance as if such a process had resulted in causing the adhesion of a darker coat of dirt than would have been produced without it; for convex, front, underlying portions of a figure are in a darker state than back parts of the same figure, though the latter are more favourably disposed for the reception of falling dirt³.

I am, my dear Dr. Milman, | Humbly and truly yours, | W. Faraday [sic]

The Very Rev. the Dean of St. Paul’s, | &c. &c. &c.