When we turn to the second great division, to the intaglio processes, we find that the recipe of the woodcut has to be just reversed to fit this new proposition. Consult the diagram of the three possibilities of printing; the cross-section of the relief-block presents a series of flat-topped ridges with valleys between them. The tops of the ridges print, the valleys are the spaces which are to appear white in the impression. The second figure, a cross-section of an intaglio plate,--an engraving on copper we will say,--shows no hills and vales, but a flat surface with a number of V-shaped cuts filled with ink. When engraving on a copper plate, we cut with the graver into the metal every line of our design that is to appear black. Wherever we want a white space we are careful to leave untouched the polished surface of the plate. Having completed the cutting-in (engraving) of our design, the plate is covered all over with printing-ink, and this is rubbed thoroughly into every furrow which we have cut, so that they are all filled flush with the surface. The surface of the plate is wiped clean. An impression taken from the plate so prepared will show us a black line for every furrow we have cut. Small wonder that the lines on the dollar bill were perceptible ridges of ink, since all the ink in the furrows of the plate is now on the surface of the paper. The theory of the intaglio processes is plainly this: wherever you want black in your design, cut lines or dots into the plate; wherever white is needed, leave the smooth surface of the plate untouched. Based upon this formula, the different intaglio processes produce their blacks in different ways; in dry-point engraving, for instance, the design is scratched into the metal by means of a sharp needle-point, the etching-needle. In tearing through the copper the needle leaves a jagged ridge of copper standing on the sides of each line, this “burr” retains some ink after the plate has been wiped clean, and gives to the dry-point line its peculiar velvety, slightly blurred appearance. The mezzotinter begins his work by roughening the whole surface of the plate with the “rocker” into myriad indentations and tiny projecting teeth of copper. The plate in this condition prints a uniform, velvety black, the deepest tone obtainable. Now by scraping away the little teeth of copper more or less completely, the design is modeled at will in varying half-tones. The high lights are obtained by burnishing the copper quite smooth again. The etcher, instead of cutting the lines of his design into the copper, trusts to the corroding action of powerful acids. Covering his plate with an acid-proof etching-ground, he draws his subject with the etching-needle, using just sufficient pressure to cut through the thin film of ground and lay bare the copper. The plate is then put into an acid bath which eats away the metal wherever a line has been laid bare. The ground is then washed off with a suitable