Filigranology is the study of watermarks. It is usually pursued in order to discover information about the date and origin for a paper-based piece of writing or a piece of art. There are several catalogues of watermarks – most notably C. M. Briquet's, Les Filigranes (1907)[1] and Edward Heawood's Watermarks, Mainly of the 17th and 18th Centuries (1950),[2] both of which include illustrations of many watermarks from dated documents. These catalogues form an important resouce for researchers.[3]