in to a sufficient depth
with nitric acid, the gilding preserving the lights from all action of
the acid. The resin grain gives a surface to the corroded parts
suitable for holding the ink, and the plate is now finished and fit to
give impressions resembling aquatint. But as silver is so soft a metal
that the surface of the plate might be expected to wear rapidly, the
discoverer proposes to shield it by depositing over its whole surface a
very thin coat of copper by the electrotype process; which when worn
may be removed at pleasure down to the surface of the noble metal
beneath, and again a fresh coat of copper deposited; and so an
unlimited number of impressions obtained without injuring the plate
itself."

If, as has been asserted, steel may be rendered sufficiently sensitive,
to take photographic impressions, to what a revolution will the art of
engraving be subject by the discovery of this process.

CHAP. VIII.

PHOTOGENIC DRAWING ON PAPER.

We shall now proceed to describe the various processes for Photogenic
drawing on paper; first, however, impressing on the mind of the
experimenter, the necessity which exists for extreme care in every
stage of the manipulation. In this portion of my work I am entirely
indebted to the works of Professors Hunt, Fisher and others.

I. APPARATUS AND MATERIALS.--Paper.--The principal difficulty to be
contended with in using paper, is the different power of imbibition
which we often find possessed in the same sheet, owing to trifling
inequalities in its texture. This is, to a certain extent, to be
overcome by a careful examination of each sheet, by the light of a
candle or lamp at night, or in the dark. By extending each sheet
between the light and the eye, and slowly moving it up and down, and
from left to right, the variations in its texture will be seen by the
different quantities of light which pass through it in different parts;
and it is always the safest course to reject every sheet in which
inequalities exist. Paper sometimes contains minute portions of
thread, black or brown specks, and other imperfections, all of which
materially interfere with the process. Some paper has an artificial
substance given to it by sulphate of lime (Plaster of Paris); this
defect only exists, however, in the cheaper sorts of demy, and
therefore can be easily avoided. In all cases such paper should be
rejected, as no really sensitive material can be obtained with it.
Paper-m