The film is assembled in the arrangement it is to be positioned onto the plate and print onto the sheets of paper (process is called stripping). An orange or goldenrod sheet of plastic or paper the size of the press plate is used. Film negatives are taped to this sheet right reading and windows are cut away so only the desired image from the film will show through. This sheet, called a masking sheet or flat is then put in a frame on top of the presensitized or image receptive aluminum plate. A glass cover is lowered down onto the flat with the film negatives on top of the plate. A vacumm pump removes the air from this frame causing a rubber blanket (not to be confused with a press blanket) to press the film negatives and plate against the glass in close, tight contact. Then a strong ultra-violet light source is turned on to expose the film image onto the plate. After this, the plate is taken out and a liquid developer is poured onto the plate to process the image so it is visible. This can be done by hand or by a mechanical plate processor.