tely: but that
is distinct from the subject of gradation, which I must not quit without
once more pressing upon you the preeminent necessity of introducing it
everywhere. I have profound dislike of anything like _habit_ of hand,
and yet, in this one instance, I feel almost tempted to encourage you to
get into a habit of never touching paper with colour, without securing a
gradation. You will not in Turner's largest oil pictures, perhaps six or
seven feet long by four or five high, find one spot of colour as large
as a grain of wheat ungradated: and you will find in practice, that
brilliancy of hue, and vigour of light, and even the aspect of
transparency in shade, are essentially dependent on this character
alone; hardness, coldness, and opacity resulting far more from
_equality_ of colour than from nature of colour. Give me some mud off a
city crossing, some ochre out of a gravel pit, a little whitening, and
some coal-dust, and I will paint you a luminous picture, if you give me
time to gradate my mud, and subdue my dust: but though you had the red
of the ruby, the blue of the gentian, snow for the light, and amber for
the gold, you cannot paint a luminous picture, if you keep the masses of
those colours unbroken in purity, and unvarying in depth.

5. Next note the three processes by which gradation and other characters
are to be obtained:

A. Mixing while the colour is wet.

You may be confused by my first telling you to lay on the hues in
separate patches, and then telling you to mix hues together as you lay
them on: but the separate masses are to be laid, when colours distinctly
oppose each other at a given limit; the hues to be mixed, when they
palpitate one through the other, or fade one into the other. It is
better to err a little on the distinct side. Thus I told you to paint
the dark and light sides of the birch trunk separately, though in
reality, the two tints change, as the trunk turns away from the light,
gradually one into the other: and, after being laid separately on, will
need some farther touching to harmonize them: but they do so in a very
narrow space, marked distinctly all the way up the trunk; and it is
easier and safer, therefore, to keep them separate at first. Whereas it
often happens that the whole beauty of two colours will depend on the
one being continued well through the other, and playing in the midst of
it: blue and green often do so in water: blue and grey, or purple and
scarlet, in s