_How to paint over or alter any part before the picture has been near
the fire._
If the parts of the picture you want to retouch are large and the
colouring dry, take a large soft hair pencil, and with water gently
moisten those places, or the whole picture if you please, and repaint
till your eye is satisfied. You might paint over, or alter any part
without moistening, but on a first trial you would not so well see
what you are about. While the picture is wet it appears very near
what it will be when fixed; when it is dry it looks like a weak dead
colouring in oil. You will see enough to judge of the general effect,
but none of the tenderer half tints will appear discernable enough to
judge of them with precision. In large pictures where the cloth will be
required stronger, a picture is kept wet with great ease and security,
by moistening it on the back with a large brush as often as there is
occasion, for the water will soon soak through the texture and take
hold of the colours; there is no danger of disturbing them on the other
side with the action of the brush, by reason of the substance of the
cloth.