"When the clean surface of a Daguerreotype plate is exposed to the action of this menstruum, particularly if warm, the white parts, or lights are not altered, but the dark parts are attacked, and chloride of silver is formed, of which an insoluble coating is soon deposited, and the action of the acid soon ceases. This coat of chloride of silver is removed by a solution of ammonia, and then the acid applied again, and so on, until the depth of biting in is sufficient. However, it is not possible, by repeating this process, to get a sufficient force of impression; a second operation is required, in order to obtain such a depth as will hold the ink, to give a dark impression; for this purpose the whole plate is covered with drying oil; this is cleared off with the hand, exactly in the way a copper plate printer cleans his plate. The oil is thus left in the sinkings, or dark bitten in parts only. The whole plate is now placed in a suitable apparatus, and the lights or prominent parts of the face are gilt by the electrotype process. The whole surface is now touched with what the French engravers call the "Resin Grain," (grain de resine), a species of partial stopping out, and it is at once bitten in to a sufficient depth with nitric acid, the gilding preserving the lights from all action of the acid. The resin grain gives a surface to the corroded parts suitable for holding the ink, and the plate is now finished and fit to give impressions resembling aquatint. But as silver is so soft a metal that the surface of the plate might be expected to wear rapidly, the discoverer proposes to shield it by depositing over its whole surface a very thin coat of copper by the electrotype process; which when worn may be removed at pleasure down to the surface of the noble metal beneath, and again a fresh coat of copper deposited; and so an unlimited number of impressions obtained without injuring the plate itself." If, as has been asserted, steel may be rendered sufficiently sensitive, to take photographic impressions, to what a revolution will the art of engraving be subject by the discovery of this process. CHAP. VIII. PHOTOGENIC DRAWING ON PAPER. We shall now proceed to describe the various processes for Photogenic drawing on paper; first, however, impressing on the mind of the experimenter, the necessity which exists for extreme care in every stage of the manipulation. In this portion of my work I am entirely indebted to the works of Professors Hunt, Fisher and others.