A detail of an Italian Renaissance atlas shows how the copperplate degraded between editions published in 1576 and 1604.

Image courtesy of Blair Hedges / Penn State

A New Hook for Dating Books

Evolutionary biologist Blair Hedges has collected antique maps and prints for years. Now he's applied his work to his hobby, devising a method for dating ancient prints that's based on the same principle biologists use to estimate when species diverged.

Bibliographers can make an educated guess about a document's age based on the accumulation of visible grime and damage. They can also try to match the watermark on the page of an undated document to a watermark with a known date, but the odds of making such a match are slim. Hoping to find a better way, Hedges, based at Pennsylvania State University in State College, reasoned that just as genes steadily accumulate mutations over time, the woodblocks and copperplates used in early printmaking probably deteriorated at a relatively constant rate.

To test this hunch, he digitized and examined 2674 Renaissance prints. In prints made from woodblocks, Hedges found that although early editions had clean, continuous lines, editions printed from the same block decades later had more gaps, presumably as a result of tiny cracks that built up as the wood aged. Copperplate prints became more faded with time at a rate that matches the corrosion of copper, Hedges reports in a paper published online 20 June in the Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences.

Because the rate of decay for both woodblock and copperplate prints is fairly constant, it can be used to date undated versions of known works, Hedges says. He tested this idea on four editions of the Italian cartographer Benedetto Bordone's Isolario, a 16th century atlas of islands. Print dates for three of the editions were known, but scholars had debated the date of the remaining edition for nearly 200 years, Hedges says. He first calibrated the "print clock" for the atlas using the dated editions to figure out how fast broken lines and other evidence of degradation accumulated in the images. Then, counting the breaks in the undated edition, Hedges estimated that it was printed in mid-February 1565 (give or take about 16 months), which would unambiguously make it the last of the four printings.

The technique "has the potential to really revolutionize how we date old objects," says David Gants, a bibliographer at the University of New Brunswick in Fredericton, Canada. If it's proved to be reliable, Hedges's technique could be used to date thousands of ancient texts and prints more accurately than is now possible, he says, adding that he's eager to try it out himself. "I'm anticipating getting down with my scanner and crack counter and establishing some timelines."

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