leaving the most minute spot of
white; and do not fill in the large pieces first and then go to the
small, but quietly and steadily cover in the whole up to a marked limit;
then advance a little farther, and so on; thus always seeing distinctly
what is done and what undone.

EXERCISE X.

Lay a coat of the blue, prepared as usual, over a whole square of paper.
Let it dry. Then another coat over four-fifths of the square, or
thereabouts, leaving the edge rather irregular than straight, and let it
dry. Then another coat over three-fifths; another over two-fifths; and
the last over one-fifth; so that the square may present the appearance
of gradual increase in darkness in five bands, each darker than the one
beyond it. Then, with the brush rather dry (as in the former exercise,
when filling up the interstices), try, with small touches, like those
used in the pen etching, only a little broader, to add shade delicately
beyond each edge, so as to lead the darker tints into the paler ones
imperceptibly. By touching the paper very lightly, and putting a
multitude of little touches, crossing and recrossing in every direction,
you will gradually be able to work up to the darker tints, outside of
each, so as quite to efface their edges, and unite them tenderly with
the next tint. The whole square, when done, should look evenly shaded
from dark to pale, with no bars; only a crossing texture of touches,
something like chopped straw, over the whole.[211]

Next, take your rounded pebble; arrange it in any light and shade you
like; outline it very loosely with the pencil. Put on a wash of colour,
prepared _very_ pale, quite flat over all of it, except the highest
light, leaving the edge of your colour quite sharp. Then another wash,
extending only over the darker parts, leaving the edge of that sharp
also, as in tinting the square. Then another wash over the still darker
parts, and another over the darkest, leaving each edge to dry sharp.
Then, with the small touches, efface the edges, reinforce the darks, and
work the whole delicately together, as you would with the pen, till you
have got it to the likeness of the true light and shade. You will find
that the tint underneath is a great help, and that you can now get
effects much more subtle and complete than with the pen merely.

The use of leaving the edges always sharp is that you may not trouble or
vex the colour, but let it lie as it falls suddenly on the paper; colour
looks m