A contrivance with moving parts for making certain astronomical calculations, sometimes made of paper and found in old geographical works. Many are very decorative. Because wall maps are easily soiled and damaged, many were discarded, and examples of early wall maps are quite scarce and often in bad condition. A design in the paper visible by transmitted light. For handmade paper, the watermark is made with bent wires placed on the rack on which the fibers are deposited to make the paper.
Designs vary from simple initials to intricate coats of arms.
Watermarks are often helpful in identifying the age of the paper. See chain marks. An image made by printing from a wooden block on which a mirror image of the design has been carved. Similar to a woodcut, but the design is engraved on the end grain, resulting in better detail and a somewhat more uniform appearance. Since the size of exposed end grain is limited by the diameter of the tree trunk, it was usually more economical to cut the design on small squares, which can be glued together for final printing.