To make sure the book is progressing properly, a proof of each flat is made by shining ultraviolet light through the negatives to expose their images onto a special light-sensitive paper. The resulting pages are called blueprints (or silverprints, bluelines, or dyluxes) because the paper and ink are blue or silver in appearance. The blueprints are then checked carefully by the publisher. If an editor or art director finds an error on a blueprint or decides to make a change, the page in question has to be rephotographed. The new negative will then be stripped onto the flat.
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