will, in the midst of
transparent tints, answer nearly the purpose of chalky body-colour in
representing the surfaces of rocks or buildings. But artifices of this
kind are always treacherous in a tyro's hands, tempting him to trust in
them; and you had better always work on white or grey paper as smooth as
silk;[236] and never disturb the surface of your colour or paper, except
finally to scratch out the very highest lights if you are using
transparent colours.

I have said above that body-colour drawing will teach you the use of
colour better than working with merely transparent tints; but this is
not because the process is an easier one, but because it is a more
_complete_ one, and also because it involves _some_ working with
transparent tints in the best way. You are not to think that because you
use body-colour you may make any kind of mess that you like, and yet get
out of it. But you are to avail yourself of the characters of your
material, which enable you most nearly to imitate the processes of
Nature. Thus, suppose you have a red rocky cliff to sketch, with blue
clouds floating over it. You paint your cliff first firmly, then take
your blue, mixing it to such a tint (and here is a great part of the
skill needed), that when it is laid over the red, in the thickness
required for the effect of the mist, the warm rock-colour showing
through the blue cloud-colour, may bring it to exactly the hue you want;
(your upper tint, therefore, must be mixed colder than you want it;)
then you lay it on, varying it as you strike it, getting the forms of
the mist at once, and, if it be rightly done, with exquisite quality of
colour, from the warm tint's showing through and between the particles
of the other. When it is dry, you may add a little colour to retouch the
edges where they want shape, or heighten the lights where they want
roundness, or put another tone over the whole; but you can take none
away. If you touch or disturb the surface, or by any untoward accident
mix the under and upper colours together, all is lost irrecoverably.
Begin your drawing from the ground again if you like, or throw it into
the fire if you like. But do not waste time in trying to mend it.[237]

This discussion of the relative merits of transparent and opaque colour
has, however, led us a little beyond the point where we should have
begun; we must go back to our palette, if you please. Get a cake of each
of the hard colours named in the note be