the drawing is removed by means of turpentine upon a piece of rag; the latter must not be too frequently changed, or a too liberal supply of turpentine made use of, or the drawing may be irreparably damaged. Unless the latter be the case the picture will reappear upon applying the roller charged with chalk ink. As may be expected, the first few impressions are seldom so perfect as the later productions. After each impression is removed the stone is at once slightly moistened. For this purpose a soft, clean sponge is suitable, or damping cloth, as supplied by dealers in printing materials. The sponge or cloth should be thoroughly wetted, wrung as dry as possible, and in that condition will possess the necessary dampness. In rolling it should be borne in mind that as in Collotype a stronger grip of the roller handles and heavy pressure with slow rolling will deposit ink upon the drawing—while, on the other hand, light quick rolling of the drawing will tend to remove the ink. To leave the stone without gumming after transferring is a convenient method of rendering the transfer more receptive of the ink. In lithographic as compared with Collotype printing the ink is reduced to a far greater extent with varnish, while both the inking slab and roller are charged far more heavily. The paper may be damp, or a dry, well-sized paper may be used. [S] A more reliable method of imparting to the surface of the paper a high gloss is to squeegee it down upon a ferrotype plate, the surface of which requires no preparation, and the risk of sticking is _nil_.—TRANS. [T] For etching extremely delicate transfers a decoction of Aleppo gall with gum is to be recommended. 15 gr. of crushed nut galls are boiled for one hour in half a kilo of water and strained through a cloth. To etch the transfer add a few drops of this solution to a solution of gum of a syrupy consistency; spread over the stone with a soft sponge, and allow to dry. CHAPTER XIX. NEGATIVES FOR PHOTO-LITHOGRAPHY. An unconditionally good negative is required for photo-lithography, and those who have not seen one produced for the purpose by an expert should endeavour as a first step to do so, or they will scarcely be likely to devote the attention necessary for producing one of a thoroughly suitable character. Not only must the lines of the copy be represented in the negative by clear glass, and the white ground of the original be represented by opacity, but the utmost sharpness of definition of the finest dots and lines to the very corners of the plate is absolutely necessary to render the negative thoroughly serviceable. To produce such a negative a lens entirely free from distortion, and capable of giving microscopic definition, is, of course, a first necessity.[U] [U] Lenses of the rectilinear or symmetrical class are best.