Make isinglass and brandy into a paste, with powdered egg-shell, very finely ground. Give it any desired colour; oil the mould, into which the paste must be poured warm. Leave the paste in the mould until dry, when its appearance strongly resembles ivory.
By holding the ivory up to the light, it will be seen whether there are any specks or holes in it; if any exist, they will be fatal to the success of the painting. It is often necessary to remove the defects found in the ivory in the state in which it is sold. To remove the marks of the saw, scrape the surface equally in every direction with an eraser, or an old razor with a fine edge, by which the marks of the saw are removed; then, with a piece of fine cork, or a roll of paper, dipped in finely pulverised and sifted pumice, or tripoli powder and water, rub the ivory with a circular motion in every direction, until the surface presents one uniform tint, but it must not appear polished; finish with a stump and a little cuttlefish powder carefully sifted; then, with a large camel-hair pencil and water, wash the surface of the ivory, and it will be ready to receive the colours. To render the ivory perfectly flat, place it between two pieces of white paper, and subject it to pressure by placing a weight upon it.
Immerse the ivory in a solution of pure phosphoric acid, sp. gr. 1.13, until it partially loses its opacity; then wash in cold soft water, and dry. This renders ivory very flexible, but it regains its hardness if long exposed to dry air. Its pliability may, however, be restored by immersion in hot water.
The ivory should be fastened at the four corners to a piece of cardboard, for the convenience of painting on; the back of the ivory should be kept perfectly clean, as any application of gum or glue to its surface destroys the transparent quality upon which its usefulness depends. After the surface to be painted on is properly cleaned, it should on no account be touched with the fingers, as the employment of oxgall to remove greasiness must be scrupulously avoided. An ivory palette is best adapted for miniature painting, because the tints appear on it the same as when worked on the miniature, a matter of considerable importance.
It is usual to paint miniatures upon ivory which is sold prepared for the purpose by the artists' colourman, after being subjected to a bleaching process by boiling, or exposure to the lays of the sun; but the bleaching can be more expeditiously performed by placing the ivory before a good fire, which will dispel the wavy lines, if they are not very strongly marked, that frequently destroy the requisite uniformity of surface. Ivory of the best quality has but few of these wavy lines, but it is frequently expedient to employ that of inferior quality. (See also ii. 33, 90, 124, 234, 358, 400.)