Small, usually brown, spots on the paper caused by mold. Foxing often results from storage in damp conditions. Gores are usually shaped like an American football. A single copy of a map. Occasionally, however, it is possible to distinguish between early and late impressions of copper engravings.
Copper is soft, and tends to wear.
Therefore early impressions tend to be darker, and sometimes-faint lettering guidelines used by the engraver are visible on impressions made early in the plate's life. Information printed on a map giving some combination of the publisher, place of publication, or date of publication. A smaller map within the border of a larger map. All impressions printed at one time without alteration of the plate belong to the same issue. Thus, if two impressions are different states, the plate has been altered and they cannot belong to the same issue.