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.
Advertisement
"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.