Sketch Book for the Artist

OBJECTS

AND

INSTRUMENTS

Light and Illusions

SEEING IS MIRACULOUS. Upside-down patterns of light on

our retinas, transmitted to the brain as chains of electrical

impulses, are translated into a world of space, atmosphere,

form, and movement. To interpret visual stimulus, our

brains search for nameable things, and are quick to

propose ideas. We will even see things that do not exist

because minimal information suggests they are likely to be

there. We only need small prompts; hence our recognition

of a cartoon face composed of three lines, and our ability

to see forms in clouds or fire.

The outermost edge of our vision, less developed than the

center, reads only movement and can often make mistakes.

Someone passes our open door, perhaps; we turn our head

but no one was there. The slightest recognition is instantly

matched to our wealth of experience and expectation, and

we can be fooled. Here we look briefly at our perception of

light and darkness and our interpretation of diagrammatic

illusions. Through these we can enjoy witnessing our own

deception and bafflement and understand certain factors

that are very useful in picture-making.

LIGHT AND SHADOW

We learn to read light and shadow in our environment as

indicators of solidity and depth of space. Artists emulate and

manipulate this effect in their pictures. Before starting a tonal

drawing of any subject, think about its illumination. Are you happy

with what you see? Does the light enhance the subject? Could

you alter and improve it? On pp.102-03 deep shadows cast across

shells make their form easier to perceive. Below, a lit photograph

of an egg shows essential points to observe in tonal drawing.

The egg's darkest region is seen

against a lighter background.

The two tones meet without

a division or outline between.

The bottom-left quarter of the egg

lightens slightly toward its "edge"

when seen against the darker

shadow cast on the paper. The rim

of light on the egg is reflected light

received from surrounding paper.

The egg's lightest region is seen

against a darker background. Run

your eye around the circumference

of the egg. See how its "edge"

smoothly changes from light

against dark to dark against light.

Below the bottom "edge" of the

egg there is a rim of light reflected

onto the paper by the underside

of the egg.

Gray squares

The perceived tone of a black white,

gray, or colored surface is never

constant. Three factors change it:

the amount of light it receives; the

adjustment of our eyes (in growing

accustomed to a level of light); and

the proximity of contrasting tones.

Here, two identical mid-gray squares

are seen against black and paler gray

squares. The small squares are

identical in tone, but do not appear

so. We perceive one to be lighter

than the other. This effect is caused

by the contrast of their surroundings.

Card experiment

To further examine changes in tone,

try this experiment. On a cloudy day,

choose a window through which you

can see the sky. Take two opaque

cards the same size, one black and one

white. Tape them to the glass. From

across the room both will appear

gray against the sky. Remove the

black card and fold and retape it with

half sticking out. Adjust the angle of the

protruding part and again step back. At

one point you will catch enough light

on the black card to make it appear

lighter than the white one.