Serendipitous Art: A Wall of Invisible Marks

Recently at the De Young Museum in San Francisco I saw a wall covered with marks—marks made by human hands—around the hand railing on a staircase. They are invisible in most lights, but, at one oblique angle and with the light coming down from above, they appear momentarily...until you move slightly and they become invisible again.

For more unintended art, see my blog Serendipitous Art.