Traditional matting is the process of compositing two different film elements by printing them, one at a time, onto a duplicate strip of film. After one component is printed on the duplicate, the film is re-wound and the other component is added. Since the film cannot be exposed twice without creating a double exposure, the blank second area must be masked while the first is printed; then the freshly exposed first area must be masked while the second area is printed. Each masking is performed by a "traveling matte": a specially altered duplicate shot which lies on top of the copy film stock.