To appraise a lithograph, consider the quality of not only the art but the paper and the artist's body of work. Also look at the appearance of the ink and the artist's signature, and look for common markings such as Benday dots and edition numbers.
Lithographs should be printed on watermarked paper. Unless preserved carefully in light-, air- and watertight conditions, older lithographs may appear discolored or stained. Any imperfection negatively impacts the value of the piece, despite its age or the popularity of the artist.
Ink used on lithographs should not be raised. The best way to assess this is by touching the piece. If that is not permitted, use a magnifying glass to examine it and determine if the ink is flat.
Benday dots occur when ink in gray areas is separated in order to prevent it from soaking through the paper. They do not occur in a true lithograph; instead, they are present in reproductions. The gray areas of lithographs are complete and are only marred by irregularities on the surface of the plate used to print them.
The artist's signature should be clearly visible and done in pencil. A lack of signature may indicate that the piece is part of a mass production and is therefore not valuable.
An edition number should also be visible. These numbers are also written in pencil. Lithographs containing the abbreviation "AP" indicate that the piece was the first production, or the Artist's Proof. The second print is numbered 001, and any further prints fall along that line. The piece's value is impacted by the number of prints made, and the most valuable lithographs are found in limited edition prints of 100 or less.