17. The _harmony_ of the whole should be studied; if the piece strikes
you as defective in this respect, place it at evening in some situation
where it will not be reached by a strong light, when the misplaced
lights and shadows will strike you more forcibly than in the glare of
day.

18. To stain your paper with a slight reddish or yellowish tint, adds to
the harmony of a sketch, yet it is a mere matter of taste; but, when it
is desired, it had better be done after the drawing is completed,
otherwise the colour risks looking patched from the rubber.[6]

[Footnote 6: Coffee has been recommended for this purpose, but delicate
and pleasing washes or glazings may be produced from burnt sienna,
yellow ochre, burnt umbre, and lake, in various combinations, and laid
on extremely attenuated by water.]

19. In _colouring_, the _sky_ gives the _ruling tint_ to the landscape;
it is absurd to unite a noonday sky, with a landscape of sunset glow.

20. From the three virgin colours, red, blue, and yellow, all the tints
of nature are composed.[7] There is not in nature a perfect white,
except snow, and the petals of some flowers.


[Footnote 7: The artist, however, cannot produce _his_ tints from those
simple colours _entirely_, but the advice once given to the writer, by a
painter, was:--"Never fancy that _many_ colours will effect your object;
a _few_ well chosen will better succeed, and be more easily managed;
half-a-dozen would, for _me_, answer every purpose." The student is
warned against _gaudy colouring_, which, if allowable in _caricatures_