Photochemical Etching Explained Production of multiple image photo-tool on transparent plastic film. Clean and pre-treat the material. Apply 1.5 mil dry PHOTO RESIST (photographically resistant) mylar layered film to the metal sheet to be etched. Expose the film via UV (Ultraviolet) light to transfer the piece part photographically to the previously treated sheet of metal. Develop the metal sheet thereby exposing the piece part image. The removal of unwanted metal by controlled acid attack. Rinse and strip the photographically resistant film from the sheet. Required forming and finishing operations.