sewing-needle, the coarser are of the size of a medium embroidery needle. It is the duty of this needle to lay bare the surface of the copper by removing the ground and rendering it ready to receive the acid. Designs are drawn in reverse. It must be remembered that they have to be printed from, so that everything facing the right hand will be facing the left in the print. Méryon, the great French etcher, turned his back on the view he was reproducing, and freely worked from the reflection in a small hand-mirror.
Let us suppose that the design has been carefully made on this sooty surface, showing the bright gleam of the copper through the cutting made by the needle. The plate is now ready for the acid bath.
The back is coated with "stopping-out" varnish, which is a varnish or Brunswick black used to protect it from the action of the acid upon the metal. If the plate be not wholly immersed in a bath, a wall of wax is built around the edge. The acid used is nitric or hydrochloric acid and chlorate of potash and water. The time the acid is allowed to act upon the plate varies from a minute to a couple of hours, according to varying conditions, such as the strength of the mordant, the metal employed, the temperature, or the quality of the result desired.
As the "biting-in" process continues, the parts which the etcher requires to be no longer eaten by the acid are "stopped-out" by the varnish. Obviously the fine lines in the sky are the first to be stopped out, and those lines which he intends to print deep black he allows the acid to act upon for a longer time.
