On this basis of line drawing the development of art proceeded. The
early Egyptian wall paintings were outlines tinted, and the earliest
wall sculpture was an incised outline. After these incised lines some
man of genius thought of cutting away the surface of the wall between
the outlines and modelling it in low relief. The appearance of this may
have suggested to the man painting his outline on the wall the idea of
shading between his outlines.

At any rate the next development was the introduction of a little
shading to relieve the flatness of the line-work and suggest modelling.
And this was as far as things had gone in the direction of the
representation of form, until well on in the Italian Renaissance.
Botticelli used nothing else than an outline lightly shaded to indicate
form. Light and shade were not seriously perceived until Leonardo da
Vinci. And a wonderful discovery it was thought to be, and was, indeed,
although it seems difficult to understand where men's eyes had been for
so long with the phenomena of light and shade before them all the time.
But this is only another proof of what cannot be too often insisted on,
namely that the eye only sees what it is on the look-out for, and it may
even be there are things just as wonderful yet to be discovered in
vision.

But it was still the touch association of an object that was the
dominant one; it was within the outline demanded by this sense that the
light and shade were to be introduced as something as it were put on the
object. It was the "solids in space" idea that art was still appealing
to.

"The first object of a painter is to make a simple flat surface appear