Moldmate identification in pre-19th-century European paper using quantitative analysis of watermarks, chain line intervals, and laid line density
Handmade laid paper has the important quality that every sheet of paper formed on the same papermaking mold retains a nearly identical imprint of the mold’s wire structure. These “moldmates” are identified by analyzing the recorded wire features, which are visible using transmitted light. When visual analysis is not sufficient to distinguish moldmates, three features of the mold’s wire mesh can be quantitatively analyzed using image processing techniques: watermark shape and placement, chain line intervals, and laid line density, for which a new method of analysis is introduced here. Using signal processing procedures, the frequency of the laid lines across a sheet of paper was found to fluctuate in a pattern unique to that mold. These quantitative methods were tested on a sample set of blank sheets from a 1536 edition of De re militari by Vegetius; computational analysis using any one of the three features was able to distinguish between four molds used in the group of papers. These results demonstrate that any of these techniques can be chosen as appropriate to determine moldmates from within a set of laid paper, regardless of size or the inclusion of a full watermark.
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