Artist proofs are often even more collectable as they are the prints that the artist created whilst proofing the edition and bear the letters 'AP' followed by the title and then the artist's signature. They are produced to the same exacting standards on museum-quality paper with archival inks. They can sometimes vary slightly from the main editions as colours will be adjusted during the original proofing. Artist proofs can still be considered part of the edition but do not form part of the numbered prints, so if there are fifty signed limited edition prints there may be a few 'AP' prints in addition to this number.