Photopolymer plates are light sensitive. On one side the surface is cured when it is exposed to ultraviolet light and other side is a metal or plastic backing that can be mounted on a base. The relief printing surface is created by placing a negative of the piece to be printed on the photosensitive side of the plate; the light passing through the clear regions of the negative causes the photopolymer to harden. The unexposed areas remain soft and can be washed away with water.