What bookdealers really mean. A dictionary by Tom Congalton and Dan Gregory (Between the Covers), with additions from other sources
A natural tanning or darkening of certain types of paper which occurs over long periods of exposure to air or ambient light. Some books, by nature of their construction, are always seen with some amount of age-toning. Some booksellers prefer the term "mellowed," a term best perhaps reserved for the feeling one gets after a few cocktails.