.

* * * * *

1. =Definition of Etching.=--To be able to get an impression on paper
from a metal plate in a copper-plate printing-press, it is necessary to
sink the lines of the design below the surface of the plate, so that
each line is represented by a furrow. The plate is then inked all over,
care being taken to fill each furrow, and finally the ink is cautiously
wiped away from the surface, while the furrows are left charged with it.
A piece of moist paper pressed against a plate so prepared, will take
the ink up out of the furrows. The result is an impression. In
_engraving proper_ these furrows are cut into the plate by mechanical
means; in _etching_ chemical means are used for the same purpose. If
nitric acid is brought into contact with copper, the acid corrodes the
metal and finally eats it up altogether; if it is brought into contact
with wax or resinous substances, no action ensues. Hence, if we cover a
copper plate with a ground or varnish composed of wax and resinous
substances, and then draw lines upon this ground with a steel or iron
style or point, so that each stroke of the point lays bare the copper,
we shall have a drawing in lines of copper (which are affected by nitric
acid) on a ground of varnish (which is not thus affected). If now we
expose the plate to the action of nitric acid for a certain length of
time, we shall find, upon the removal of the ground by means of benzine,
that the lines have been _bitten into_ the plate, so that each line
forms a furrow capable of taking up the ink. The depth and the breadth
of the lines depends upon the thickness of the points used, and upon the
length of time allowed for biting; or, in other words, by varying the
size of the points and the time of exposure the lines may also be made
to vary. This is the whole of the _science_ of etching in a nutshell.

2. =Requisites.=--The following tools and materials are the only ones
which are absolutely necessary for a first experiment:--

1. A COPPER PLATE on which to execute your etching. Do not waste your
money on a large plate. A visiting-card plate is sufficiently large. If
you happen to have an engraved plate of that kind, you can use the back
of it. If you have none, get one at a card-engraver's. The price ought
not to be over fifteen cents. If you do not live in any of the large
cities named above, or cannot find a card-engraver, send fifteen cents
in stamps to Mr. Geo. B. Sharp,