ABSTRACT
White paper, or white leather moistened with a solution of nitrate of silver, undergoes no change when kept in a dark place; but on being exposed to the day light it speedily changes colour, and after passing through different shades of grey and brown, becomes at length nearly black. When the shadow of any figure is thrown upon the prepared surface, the part concealed by it remains white, and the other parts speedily become dark. For copying paintings on glass, the solution should be applied on leather; and, in this case, it is more readily acted upon than when paper is used. The copy of a painting, or the profile, immediately after being taken, must be kept in an obscure place. In comparing the effects produced by light upon muriate of silver, with those produced upon nitrate, the muriate was the most susceptible, and both were more readily acted upon when moist than when dry, a fact long known.
