The author attempts correlating the dates of unwatermarked papersfrom the earliest era of European papermaking with chain lineintervals and laid line frequencies.
The basis of the study of watermarks is that at a given period oftime a specific paper mill would have on hand a limited number ofpapermaking molds, and these molds had a finite useful life.
Several theories have been proposed.
Identification Marks- like Trademarks of today.
This seems unlikely since there were so many more watermarks than papermakers.
An English appendix "The Paper Mills inthe Provincie of North-Holland" includes an excellent sectionentitled "Filigranology as an auxiliary science in the aid ofhistory." Voorn's methods of studying papers in archives makes hiswatermark dates more certain, but means watermarks on paper commonlyused for fine art are not always represented.