What you MAY have is a box of litho printing plates. If so, these would be exposed to intense UV light under a "litho" negative of the typesetting artwork, and then "developed" by rubbing all over with a chemical (forgot the name). The parts that received the UV light (clear parts of the negative) remain, and the unexposed areas are chemically removed. The parts that remain on the aluminum are very sensitive to soaking up ink. On the press, the water fountain roller coats the plate with a thin film of water that is repelled from the developed image areas, and the ink rolllers contact the whole plate with a film of ink, but it only sticks where the image areas is. This image area is transferred thru a rubber blanket intermediate roller to the final sheet of paper as it goes thru the press thus creating PRINTED matter. Almost every piece of printed paper in your household, books, magazines, brochures, sales flyers, newspapers, junk mail, non-junk mail, packaging on products, etc., are printed in this manner. There is a plate made for each color in color "process" printing. The colors are printed in succession, including black.
