| This exhibit
is illuminated with pure yellow (mono-chromatic) light from a sodium
vapor lamp. This light passes through two glass plates on top of
each other. Light reflected from the two surfaces in the "inside"
of the glass sandwich interfere with each other. The thickness of
the air between the plates determines the interference pattern.
Pressing on the plates changes the pattern. Colored prints look
black and white under the sodium lamp and full color under a white