The Biologist as Bibliosleuth

Gigi Marino
December 04, 2006

Blair Hedges has a fine eye for detail. He notices things that other people don't—like a tiny lizard smaller than a match stick sitting among leaves and roots in a forest in the Dominican Republic. Hedges has discovered or co-discovered 55 new animal species, including the world's smallest frog and lizard. (Recently he discovered another "smallest animal" but is careful not to reveal it publicly until it is published.) It's not surprising, then, that when the Penn State biologist set out to determine the publication date of an undated Renaissance atlas—which has eluded rare-books historians for two centuries—he developed a statistical method for dating antique art prints and books by looking at them in ways no one had ever done before.

Hedges' quest began a few years back when he was working on his Web site of antique maps of the Caribbean (Caribmap). This is the tropical region where, for the last 25 years, he has conducted much of his fieldwork as a herpetologist (a person who studies amphibians and reptiles). He had posted maps from Italian cartographer Benedetto Bordone's book Isolario (which roughly translates to "island book" in Italian). "I was recording the historical details," he says. "This book was printed in 1528, 1534, 1547, and in an undated edition. For 200 years, people argued about that undated edition. I couldn't believe that they would say, '1530s or 1570s,' and would be 40 years off. I thought that there's got to be something in the prints themselves to tell you when the book was printed."

For years, book antiquarians surmised publication dates by looking at the paper or watermarks. Hedges had a different idea. He examined the prints, which showed line breakage from the woodblocks used to print the books. He surmised that the woodblocks cracked naturally as they aged during storage, in between printing runs, not during the actual printing process, which had been a commonly held belief. Says Hedges, "I thought, maybe these little breaks in the wood are like genetic mutations. And that's what I do in my real life, use genetic mutations to find when species split. So, if they're random, then this could be like a geologic, or radiometric, clock or a molecular clock, both also based on random change."

Print clock
Courtesy Blair Hedges

A borrowed idea

At a glance, the idea of a molecular clock may seem paradoxical, for its timekeeping mechanism is based on stochastic events, or randomness. First proposed by Linus Pauling and Emile Zuckerkandl in 1962, molecular clocks track minor mutations in DNA, which occur at a constant rate. However, these mutations also occur randomly, and it's the pattern of randomness that can be quantified, analyzed, and used as a predictor. Researchers like Hedges are able to look at these genetic mutations occurring over hundreds of millions of years, compare them against the fossil record, and determine when species split along the evolutionary tree. Once considered controversial, molecular clocks are now standard tools for evolutionary biologists and even virologists who use them to plot new viral epidemics.

For Bordone's maps, Hedges used high-resolution scans of the prints and image-analysis software that quantified the number of breaks in the lines. He says, "I started doing the numbers and couldn't believe what I was seeing because I was finding constant change between the dated editions, which meant there was a clock going on." Through this analysis, Hedges determined that the undated Bordone was published in February, 1565, give or take 16 months. He thought, "Wow, if it's possible to date this book, then you can date any book."

The very first books of the Renaissance were printed from woodblocks, but copper plates soon followed toward the end of the 16th century. The media are different. Woodblocks are carved, and copper plates are engraved or etched, so the kind of line breakage that Hedges observed in prints made from woodblocks does not correlate to copper-plate printing. But Hedges was undeterred. Instead of looking for line breaks, he measured the overall amount of black ink in each print, and found that copper-plate prints from later editions were paler because of thinner lines. Copper-plate prints also are subjected to a process that woodblocks are not—regular polishing to remove nicks and corrosion. In his research, Hedges discovered in printing manuals from the 1500s and 1600s that the copper plates were cleaned before printing each new edition with a variety of abrasives, including pumice, charcoal, and bread crumbs. The polishing was done to remove wear and tear on the copper plates so that those nicks and corrosion would not hold ink and be printed.

Hedges was surprised at his own results: "I got into copper plates and couldn't believe that the copper plates changed exactly the same way, constantly." The pattern of deterioration in both the woodblocks and copper plates produced a general clock despite the fact that the two relied on completely different mechanisms for change. However, in both cases, the changes were completely random and continuous. The only way for a clock to develop, stresses Hedges, is that if the copper corroded in a fairly constant rate, and the printer eroded only as much corrosion as had developed since the last printing—a rather delicate balance that continued for decades, as plates were expensive to make, and printers used them for up to 50 years or more. "Having all those parameters come to play," he says, "I am amazed at how much of a correlation there was." Thus was born the "print clock."

Blair Hedges
AP Photo/Pat Little

Blair Hedges

Nailing it down

True to the scientific method, Hedges sought to replicate his results and increase his data set. In 2005, between teaching and research obligations, he visited 20 rare-book rooms in libraries on the East Coast. "In one case, I drove to Yale, found what I needed, and drove back in the same day," he says. "That's how dedicated I was to this project." He also acquired a number of prints from Italy, and even some information from the Vatican, with the occasional help of his Italian doctoral student Fabia Battistuzzi for telephone translations. Battistuzzi was happy to assist but confused about the relationship between genetics and rare books, Hedges remembers.

His final data set included 2,674 Renaissance prints, made from both woodblocks and copper plates. And the results were constant and conclusive. In woodblock prints, the number of line breaks increased over time, and in copper-plate prints, the lines became paler, both in a regular clock-like manner.

Hedges' study appeared in the journal Proceedings of the Royal Society A: Mathematical, Physical, and Engineering Sciences in June 2006. Since then, his print clock has garnered plenty of attention from librarians and bibliophiles, including one critic who claimed that Hedges' theory was all wrong, that the lines made from copper plates did not become paler because of random change but because the copper plates were becoming thinner from the compression of the printing process itself. Hedges says that basic physics will tell you this is not the case—just put a copper penny on a train rail and see what happens. "The copper squishes," and the lines get wider. But to prove the point, Hedges took some copper plates, engraved them with a burin, a tool just like the ones that Renaissance artists used, placed the plates between boards, and drove over them with his 6,000-pound Volvo SUV. When the plates did not flatten, he then hit them with a sledgehammer until they did, proving that the lines widened and did not get narrower. He has not heard from any detractors since.

Hedges funds his own research with the print clock, and his passion for this project stems from a lifelong love of old maps. During his undergraduate years at George Mason University, he worked at the U.S. Geological Survey in Reston, Va. He says, "After work I would visit the printing plant, where they would let me have discarded maps containing minor defects, such as a smudge of ink on a beautiful map of Hawaii with all the valleys and waterfalls, and I'd take them home with me." He still has dozens in his attic, added to a collection of old Caribbean maps that he's been collecting seriously for the last decade.

Courtesy Blair Hedges

Engraving a copperplate: A steel burin carves a triangular-shaped groove (one-fifth of amillimeter) in a polished copperplate, pushing up a sliver of copper about the thicknessof dental floss.

While others in the rare-book world are interested in the print clock, and some are using it, it will take time before those studies are published. Hedges says, "I hope people start using it immediately, but with any new method, you need a lot of evidence and data to convince an entire field. If a half-dozen more studies of copper plates and woodblocks show it to be useful, perhaps then it will become an accepted method.

"Maybe I'll do them all myself in the next 10 years or so."

S. Blair Hedges, Ph.D., is professor of biology in the Eberly College of Science; His Print Clock Web site includes both a general overview of the dating process and a pdf version of his technical paper on the subject.

Gigi Marino is editor ofBucknell Worldand a writer and poet in Lewisburg, Pennsylvania.

Last Updated December 04, 2006