_Of the colours and their preparation._
All colours used in oil painting are fit for this manner, and no
others. There are a few that ought to be omitted; for reason see the
list of colours.
Grind all your colours very fine with simple water, allot to every
particular colour a distinct vessel, such as gallipots, pans, &c. From
your colours so ground, compose all the different principal tints, as
the nature of your intended work shall require.
But, as most of the colours acquire a deeper hue when moistened, and
some deeper still when fixed with wax, it will be necessary, to prevent
perplexity in the execution, to have a guide for retouching, either
when the picture is finished and dry, before the operation of the fire,
or after it is fixed; for this purpose you may, before you go to work,
use the following expedient.
Take two slips of cloth about a foot long, and three or four inches
wide, wax them as before mentioned, then upon the one slip paint
of every one of your entire colours[6] about an inch high over the
whole width of the cloth, and with your tints already composed do
the same upon the other piece of cloth, according to their order and
degradation;[7] mark every tint with a number, such as 1, 2, 3, &c.
write down upon a paper every number, and what it is composed of. This
done and your colours so applied dry, cut your cloth across all the
tints from top to bottom in two equal parts; bring one half of each
near the fire, and by melting the wax fix them, the other two halves
you keep as they are unfixed.
By rejoining and comparing them together, you may judge what strength
every tint will acquire, and by their reciprocal references you will
be enabled to alter or imitate, deepen or heighten with certainty, any
tint, either before or after the colours are fixed.
In painting be not sparing; the greater body of colours you employ,
the better and brighter your work will appear; you may give greater
freedom to your pencil, blend and sweeten your colours better than in
any other way of painting.