In order to get an impression on paper from a metal plate the lines of the design have to be sunk below the surface of the plate, and each line is represented by a furrow. The plate is then inked all over so that these furrows are filled. The superfluous ink on the surface is carefully wiped away, and the plate is then ready for printing. A sheet of damp paper is, by means of a copper-plate printing press, pressed upon the plate. The result is a print.
If a piece of copper be placed in nitric acid the metal is corroded, and if left long enough in its bath it would be eaten up altogether. Nitric acid does not touch wax nor resinous substances. These two facts govern etching.
A metal plate is held in a hand-vice over a flame till it is sufficiently hot to receive the etching-ground which is applied to it. This etching-ground consists of a mixture of asphaltum, burgundy-pitch, and beeswax. By means of a dabber of cotton wool made in a ball, covered with a piece of silk, it is applied to the plate, the hot metal causing the "ground" to ooze through the silk covering and deposit itself evenly on the surface of the plate. The ground can also be used cold as a paste dissolved in oil of lavender and applied with a roller, or, when dissolved in chloroform, poured over the plate.
After the etching-ground has been laid the plate is held face downwards over a bundle of lighted tapers and coated with a deposit of smoke, leaving it with a fine black surface.
The plate is now ready for etching. Etching needles are used; the finer are of the thickness of a
