A geneticist uses an algorithm for speciation to solve mysteries of undated editions of hand-printed books.

Woodblock print of Jamaica showing changes over time. Above is a print from the first edition of Bordone’s Isolario in 1528, and below is a print made from the same woodblock in 1565 (fourth edition) showing breaks in lines (arrow heads). Image courtesy of Blair Hedges, Penn State

In 1528, Italian cartographer Benedetto Bordone published Isolario, a hand-printed book featuring exquisite maps of the world’s islands. It represented a significant milestone in map-making. Over the following decades—once in 1534 and then again in 1547—additional editions of the landmark atlas were printed, including one that was never stamped with a date. That edition of Isolario caused historians to squabble for years over its print date, placing it anywhere between 1537 and 1570. 

But now Blair Hedges, an evolutionary biologist at Pennsylvania State University, has borrowed a technique from biology that could resolve this debate—and several others like it.

Over years of fieldwork in the Caribbean, Hedges amassed maps of the sea’s islands. As his collection grew, he realized that many of his maps were undated, and he learned that their production dates had been fiercely disputed for years, without resolution.

Hedges also keyed in on a useful fact about the prints: The Renaissance-era tools employed to make them—either an inked copper plate with a design engraved into it or an inked woodblock with a carved, raised design—were reused over many years to produce multiple print runs of a map or book.

“I noticed in these prints that over the different editions, when printers would print over the decades, they would show signs of the printing device deteriorating,” Hedges said. “That kind of narrowed down at least the order of the printing.”

He also realized that later editions of prints made with a woodblock showed more cracks and gaps in the inked lines than earlier editions, while later editions of prints produced by copper plates were fainter, with thinner lines, than their predecessors. He wondered whether the progressive deterioration of printing blocks and plates could be used to more closely pinpoint the dates when certain editions were produced. 

So, he turned to his expertise: genetics.

In his research, Hedges estimates the timing of speciation through DNA sequence data, using a technique that tracks the genetic mutations that crop up in a species over generations. Even though mutations pop up randomly, scientists can average millions of years of data to determine a species’ average rate of genetic mutation. This allows biologists to take samples of DNA from animals living today and estimate when certain mutations appeared, as well as when one species diverged from another. 

“The methods we have for dating books right now are really approximate. They’re hit or miss.”

Hedges thought this “biological clock” method could solve his print-dating problem.

“I looked at these prints and thought, ‘These are just random errors in the printing devices just like random errors in DNA,’” Hedges said. 

He spent more than a year examining thousands of Renaissance prints, comparing different editions of images that had been printed at known dates to determine the rate at which errors materialized. 

What he found was striking: Whether the print was made with a wood block or a copper plate, print quality deteriorated at a constant rate over time.

“There seems to be a linear relationship with time and the deterioration of these printing devices,” said Hedges, who published his findings in the June 21st issue of the Proceedings of the Royal Society

Using computerized image analysis tools, researchers can calculate the rate of change in print quality over the period of time that separates two or more dated prints, said Hedges. The resulting rate, and an analysis of the quality of the undated print, can then be used to determine how much time separates the creation of dated and undated prints.

Working with this method, Hedges was able to estimate that the fourth Isolario edition was printed in 1565, give or take a year.

“The methods we have for dating books right now are really approximate. They’re hit or miss,” said David Gants, a specialist in technology and the humanities at University of New Brunswick in Canada. “After reading [Hedges’] paper, I thought ‘Oh! I want to do that!’”

The print clock. In these models, close-ups of a carved woodblock (above) and engraved copperplate (below) are shown, corresponding to a curved black line on the print behind it, at two time periods. Over time, cracks develop in the woodblock resulting in line breaks on prints. With copperplates, erosion of the surface produces thinner groves and thinner lines in prints. For both, the change is time-dependent. Image courtesy of Blair Hedges, Penn State

One of these approximation methods involves matching the watermark on a print’s paper to a database of when certain watermarks were used. But many watermarks are not in the database, and this method dates the paper, not the print, which may have been made long after the paper.

Hedges’ technique works because it addresses the deterioration of the plates and woodblocks, which is time dependent and not, as was more commonly thought, dependent on the number of press runs. That means the plates and woodblocks deteriorated in between press runs, not during them.

“It kind of goes against logic,” Hedges said. “The printing press is a giant metal roller that squished the plate into a metal frame. The literature says the deterioration occurs because the great pressure of the press would squish the metal like pizza dough being squished down with a roller.”

Though it may be counterintuitive, Gants said time-dependent deterioration makes sense. In the days before electric heat and air conditioning, woodblocks would crack as they expanded and contracted throughout cold winters and hot summers. According to Hedges, as copper plates sat in storage between printings, their surfaces corroded over time—before being used again, printers would wipe off corroded layers, producing progressively fainter and thinner images. 

Hedges plans to continue his print-dating hobby; he estimates that there are a few hundred thousand hand-printed books that remain undated, including Shakespearean prints.

The hope is that book and art scholars will also embrace his new method.

“Fundamentally, there should be no technology or skill barrier for anyone using this,” said Gants. “It’s really a matter of acceptance of the scientific method within the humanistic community. That’s the crunch. If it’s reproducible, it will revolutionize how we date books.”

Originally published July 6, 2006

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