SISTO BADALOCCHIO (1581–1647). God separating Light from
Darkness (after Raphael). 1607. ETCHING is an intaglio process
in which the image is etched into a metal plate. The polished
plate is covered with an acid-resistant layer, which is usually
composed of resin, wax, and asphalt. The image is drawn into
that layer with an etching needle. For the drawing to be more
distinct, the plate is first covered with soot. Then it is
immersed in an acid (the zinc plate — in nitric or hydrochloric
acid; the copper, steel, or iron plate — in ferric chloride),
which etches the image into the surface of the plate. After
removing the acid-resistant layer, the plate is covered with
printer's ink. As the plate is rubbed all over, the ink remains
only in the etched lines. The image is then printed from the
plate onto paper by means of a printing press. An etching plate
can be bitten many times, and the method that will be chosen
should be considered already in the phase of drawing the image.
If biting only once, needles of var