The great use in copying, if it be at all useful, should seem to be in
learning to colour; yet even colouring will never be perfectly attained
by servilely copying the mould before you. An eye critically nice can
only be formed by observing well-coloured pictures with attention: and by
close inspection, and minute examination you will discover, at last, the
manner of handling, the artifices of contrast, glazing, and other
expedients, by which good colourists have raised the value of their
tints, and by which nature has been so happily imitated.

I must inform you, however, that old pictures deservedly celebrated for
their colouring are often so changed by dirt and varnish, that we ought
not to wonder if they do not appear equal to their reputation in the eyes
of unexperienced painters, or young students. An artist whose judgment
is matured by long observation, considers rather what the picture once
was, than what it is at present. He has acquired a power by habit of
seeing the brilliancy of tints through the cloud by which it is obscured.
An exact imitation, therefore, of those pictures, is likely to fill the
student's mind with false opinions, and to send him back a colourist of
his own formation, with ideas equally remote from nature and from art,
from the genuine practice of the masters and the real appearances of
things.

Following these rules, and using these precautions, when you have clearly
and distinctly learned in what good colouring consists, you cannot do
better than have recourse to nature herself, who is always at hand, and
in comparison of whose true splendour the best coloured pictures are but
faint and feeble.

However, as the practice of copying is not entirely to be excluded, since