St. Paul's Bibliographies, 1994. Singleton Leaf A leaf with no conjugate . Thus every page has two sides, the recto and the verso. See Recto . Watermark A design of semitransparent lines visible near the middle of the inner margin when held to the light.
Watermarks are useful in determining the maker of the paper and the place of manufacture.
Wire Lines Thinly spaced vertical lines visible when holding a page to the light.