If you lay on a solid touch of vermilion, and after it is quite dry,
strike a little very wet carmine quickly over it, you will obtain a much
more brilliant red than by mixing the carmine and vermilion. Similarly,
if you lay a dark color first, and strike a little blue or white
body-color lightly over it, you will get a more beautiful gray than by
mixing the color and the blue or white. In very perfect painting,
artifices of this kind are continually used; but I would not have you
trust much to them: they are apt to make you think too much of quality
of color. I should like you to depend on little more than the dead
colors, simply laid on, only observe always this, that the _less_ color
you do the work with, the better it will always be:[47] so that if you
had laid a red color, and you want a purple one above, do not mix the
purple on your palette and lay it on so thick as to overpower the red,
but take a little thin blue from your palette, and lay it lightly over
the red, so as to let the red be seen through, and thus produce the
required purple; and if you want a green hue over a blue one, do not lay
a quantity of green on the blue, but a _little_ yellow, and so on,
always bringing the under color into service as far as you possibly can.
If, however, the color beneath is wholly opposed to the one you have to
lay on, as, suppose, if green is to be laid over scarlet, you must
either remove the required parts of the under color daintily first with
your knife, or with water; or else, lay solid white over it massively,
and leave that to dry, and then glaze the white with the upper color.
This is better, in general, than laying the upper color itself so thick
as to conquer the ground, which, in fact, if it be a transparent color,
you cannot do. Thus, if you have to strike warm boughs and leaves of
trees over blue sky, and they are too intricate to have their places
left for them in laying the blue, it is better to lay them first in
solid white, and then glaze with sienna and ocher, than to mix the
sienna and white; though, of course, the process is longer and more
troublesome. Nevertheless, if the forms of touches required are very
delicate, the after glazing is impossible. You must then mix the warm
color thick at once, and so use it: and this is often necessary for
delicate grasses, and such other fine threads of light in foreground
work.