ke of Prussian blue, and passes down into pure
white paper at the end of your column, with a perfectly smooth gradation
from one into the other.

You will find at first that the paper gets mottled or wavy, instead of
evenly gradated; this is because at some places you have taken up more
water in your brush than at others, or not mixed it thoroughly on the
plate, or led one tint too far before replenishing with the next.
Practice only will enable you to do it well; the best artists cannot
always get gradations of this kind quite to their minds; nor do they
ever leave them on their pictures without after touching.

As you get more power, and can strike the colour more quickly down, you
will be able to gradate in less compass;[205] beginning with a small
quantity of colour, and adding a drop of water, instead of a brushful;
with finer brushes, also, you may gradate to a less scale. But slight
skill will enable you to test the relations of colour to shade as far as
is necessary for your immediate progress, which is to be done thus:--

Take cakes of lake, of gamboge, of sepia, of blue-black, of cobalt, and
vermilion; and prepare gradated columns (exactly as you have done with
the Prussian blue) of the lake and blue-black.[206] Cut a narrow slip
all the way down, of each gradated colour, and set the three slips side
by side; fasten them down, and rule lines at equal distances across all
the three, so as to divide them into fifty degrees, and number the
degrees of each, from light to dark, 1, 2, 3, &c. If you have gradated
them rightly, the darkest part either of the red or blue will be nearly
equal in power to the darkest part of the blue-black, and any degree of
the black slip will also, accurately enough for our purpose, balance in
weight the degree similarly numbered in the red or the blue slip. Then,
when you are drawing from objects of a crimson or blue colour, if you
can match their colour by any compartment of the crimson or blue in your
scales, the grey in the compartment of the grey scale marked with the
same number is the grey which must represent that crimson or blue in
your light and shade drawing.

Next, prepare scales with gamboge, cobalt, and vermilion. You will find
that you cannot darken these beyond a certain point;[207] for yellow and
scarlet, so long as they remain yellow and scarlet, cannot approach to
black; we cannot have, properly speaking, a dark yellow or dark scarlet.
Make your scales of full yel