Ink soaked sponge

A 3" x 4" x 2" wooden box within which is an ink soaked sponge. Touching the sponge causes inky hand prints to appear on whatever that person has touched for the last hour. The inky prints fade in an hour and can't be washed away. The sponge dries out after one use and must then be refilled with a full vial of ink before it can again be used.