Myth-busting early modern book illustration, part one

The example that immediately came to my mind was the notion that copper plates wear out because the intense pressure from the rolling press compresses the soft copper over time (though I believe the term I used in the workshop was “squooshes” rather than “compresses” since it’s rare that a good example and proper vocabulary come to my mind at the same time). ¹

A rolling press, for printing from intaglio plates

This compression, according to the hypothesis, is the reason why prints in later editions of a book are paler than those in earlier editions. Compare a detail of a ship from the 1552 (first) edition of L’isole piu famose del mondo and the 1556 (second) edition. The area of cross-hatching on the sail makes a particularly good example of engraved lines becoming thinner (paler) and shorter over time:

Detail of a ship’s sail from the upper right of the “Spagnola” map in Thomaso Porcacchi, L’isole piu famose del mondo… 1572 edition (on left) and 1576 edition (on right). Click image to open a pan-and-zoom window.

While it is true that copper is soft (or else you couldn’t cut lines into it with hand tools) recent studies by S. Blair Hedges, a scientist at Penn State, demonstrate that plates did not compress with use, and that even if they had, lines would become longer and wider, not shorter and thinner (imagine rolling out pie dough, marking an “X” on it, then using the rolling pin some more. The “X’ will stretch and grow). Instead, Hedges’ work supports the idea that plates wore out through erosion when they were polished for re-use after storage. ²

Generalized diagram showing change in width of an engraved triangular-shaped groove in a metal (copper) plate through time (four editions), and the printed lines produced by that groove. The cross-section of the ink-filled groove is black. Before each printing, the plate surface was polished (eroded) to remove nicks and corrosion, narrowing the width of the triangular groove. (Copyright S. Blair Hedges; made available for educational purposes)

Lines become thinner not in relation to the number of impressions taken from the plate, but in relation to the time between printing sessions. ³ Using digital images and scientific software designed for image analysis, it is possible to gather data from multiple copies of different dated editions of a print, graph them to show where the different editions cluster in terms of line density, then see where data collected from an undated edition of a print falls within the time scale. Hedges was able to show similar correlations between time and image deterioration in woodcut illustrations by counting line breaks (the result of increasing cracks and losses in the raised surface of the block).

Why isn’t this information better-known among people who teach and study the history of the book? Perhaps the most obvious reason is that it’s hard enough to keep up with academic journals such as Renaissance Quarterly and Printing History, so when Hedges’ work appeared in Proceedings of the Royal Society A : Mathematical, Physical, and Engineering Sciences in 2006 ⁴ and Proceedings of  SPIE (the international society for optics and photonics) in 2008 ⁵ it didn’t exactly find its audience.

For a general overview of the research and practical how-to instructions, see The Print Clock: A method for dating early books and prints.

What else might we learn about early modern prints from a massive database of crunchable numbers? Blair Hedges reports that “discriminant function analysis” of three different sets of early modern prints and three different Renaissance maps “was able to group art prints from different sets and maps based on different mapmakers” based on the density of the line work. ⁶ This sounds very much like the kind of statistical analysis of word patterns and types already familiar to many in literary studies.

Can the study of book illustrations give anything back to the scientists? You know those worm holes that show up as white spots in woodcuts?

As a print collector, Blair Hedges knows worm holes, and as a biologist, he knows worms (or rather, the wood-boring beetles that make what we refer to as worm holes). It turns out that different species of wood-boring beetles make different-sized holes, so he started counting and measuring white spots on book illustrations known to have been printed in particular places at particular times. It turns out that two species whose current European habitats overlap almost completely were clearly separated until modern times, one in northern Europe, the other in southern Europe. ⁷ There must be plenty of other opportunities for studies like this, it’s just that people in the humanities and the sciences need to pool our knowledge. Let’s get busy!