t as if the plate had never yet been touched
by the needle.

44. =Transparent Ground for Retouching.=--The white or transparent
ground or varnish[11] admirably allows all previous work to show
through. It is preferred to the ordinary ground for working over parts
that have been insufficiently bitten, on account of its transparency,
which leaves even the finest lines visible, while under the ordinary
ground these lines might be lost entirely. It will be an easy matter for
you to combine the new work with the old; the very slight shadow thrown
on the copper by the transparent ground will give a blackish appearance
to your lines, which may serve as a guide to you, and, with your proof
before your eyes, you will readily succeed in finding the places which
need retouching. To make assurance doubly sure, you can indicate the
retouches on your proof with a lead-pencil.

The transparent ground has occasionally been found to crack and scale
off, when left in the bath for a long while, or when strong acid is
used. But as you are only going to use it for light and, consequently,
short biting, you need not fear this danger. Another inconvenience,
which may easily be prevented, consists in the presence of small bubbles
of air, which appear on the varnish as soon as it begins to melt. Heat
the plate just to the proper point of melting, and dab it vigorously for
some length of time, until the varnish cools; then hold the back of the
plate flat to the fire; the varnish melts again, and the rest of the
bubbles disappear. If some of them should prove to be obstinate, cover
them very lightly with the brush, as otherwise the acid will penetrate
through the passages thus left open, and will make little holes in the
copper, which, on removing the varnish, will cause an unpleasant
surprise. You shall hear more of this further on.

45. =Ordinary Ground used for Retouching.--Biting the
Retouches.=--Ordinary etching-ground, such as we used in the first
instance, does not show the work previously done as well as the
transparent ground, but the later additions are seen all the better on
it. It may be used in its natural state, or it may be smoked. It is
preferable to the transparent varnish, whenever the work already
achieved is deeply bitten, and hence easily seen.

In the present case my advice is that you use the ordinary ground.
Having made your retouches, introduce your plate into the bath, and
proceed as before, by partial biting, endeav