Progression proofs are proofs, or test prints, that are used by the printers to test the colors and color alignment before final printing of art prints, posters, cereal boxes, postcards or whatever they are printing. The purpose of such proof printing is to identify and correct any errors and make sure everything looks good before you print the final product. You don’t want to print 5,000 final movie posters then realize you did a dumb miscalulation that made the colors look horrible or printed the text upside down. You want these types of errors weeded out in the proofing stage.
There was a series of progression proofs for a print, with each proof testing a unique color combination. For example, one proof was printed in black and white, the next black and yellow, the next blue and red, and so on. The set will show the prints in a variety, or progression, of colors. Progression proofs are often also called ‘color separation proofs,’ or ‘color separation tests,’ all which are acceptable names.
The below shows a progression proof set for a 1975 Hostess baseball card, printed by the famous Topps Chewing Gum Company of New York City. Each card has a different color combination.