An individual archive: Rembrandt's Prints
Nancy Ash and Shelley Fisher, Watermarks in Rembrandt's Prints (Washington, DC, 1998) is a catalogue of watermarks, with beta radiographs, found in copies of Rembrandt's prints held at the National Gallery of Art in Washington, DC, and a number of other collections. This focused study on a specific archive - by which I mean the documents produced by Rembrandt's studio, not a particular modern collection - has provided new information about Rembrandt's production of etchings.
For example, copies of some etchings that were originally designed as much as twenty years apart were made on the same paper. The most likely explanation for this is that he reprinted old etchings when the demand arose; Ash and Fisher claim (p. 16) that, "for Rembrandt, reprinting was not an occasional activity but a vital part of his working method."
As well as providing an insight into Rembrandt at work, the study of these watermarks can be used to date individual prints. Of course there are difficulties involved in this work, notably in the question of how long paper may have remained in the studio before being used.
A number of the plates from which impressions were made survived after Rembrandt's death, leaving open the possibility of posthumous printing. These can be identified from watermarks, at least in cases where the paper was not produced until after the artist's death. Ash and Fisher have found many examples of this.
The approximate date of a watermark can also be used, alongside stylistic and other evidence, to estimate the date of an undated print.