not wait till the varnish has become
too dry before you execute the retouches, which, of course, must also be
bitten in as usual. Mixed with lamp-black, the stopping-out varnish
allows even the finest lines to be seen, which would not show as well if
the varnish were used in its natural state. Many engravers use this
varnish instead of the transparent ground.

47. =Partial Retouches.--Patching.=--For partial retouches and for
patching the stopping-out varnish is also used, but in a simpler and
more expeditious way. Cover the part in question with a tolerably thick
coat of varnish, and when you have finished your retouch, slightly
moisten the lines with saliva, to prevent the few drops of acid which
you supply from your bath with the brush from running beyond the spot on
which they are to act. If pure acid is used,--which is still more
expeditious,--the effervescence is stopped by dabbing with a piece of
blotting-paper, and the operation is repeated as long as the biting does
not appear to be sufficient. For very delicate corrections it is
advisable not to wait until the first ebullition is over; but it must be
left to the feeling to indicate the most opportune moment for the
application of the blotting-paper. If you proceed rapidly and
cautiously, you can obtain extremely fine lines in this way, as you have
had occasion to see under other circumstances (see paragraph 40, p. 25).

You may recollect that I spoke of lines which had not bitten: I alluded
to this spot in the middle of the bridge (see Pl. I^_a_). You did not
bear on your needle sufficiently, and hence it did not penetrate clear
down to the copper; consequently, after having compared the proof of the
first state with the original (Pl. II.), you must do the necessary
patching according to the instructions just given to you.

48. =Dry Point.=--Whenever it is necessary to retouch, or to add to very
delicate parts of the plate, such as the extreme distance, or any other
part very lightly bitten, it is safer to use the _dry point_, as in such
cases retouching by acid is a most difficult thing to do. The tone must
be hit exactly, and without exaggeration.

Your plate offers an opportunity for the use of the dry point: the sky
and the mountain are partly etched; you can improve them by a few
touches of the dry point.

The dry point is held in a perpendicular position, and is used on the
bare copper. It must be ground with a cutting edge, and very sharp, so
that