Draw a figure with weak gum-water upon the surface of a convex mirror.
The thin film of gum thus deposited on the outline or details of the
figure will not be visible in dispersed daylight; but when made to
reflect the rays of the sun, or those of a divergent pencil, will
be beautifully displayed by the lines and tints occasioned by the
diffraction of light, or the interference of the rays passing through
the film with those which pass by it.