From Scientific American:
A molecular biologist has borrowed a technique from genetic science to date hand-printed art. The so-called print clock method, developed by Blair Hedges of Pennsylvania State University, could help historians and collectors pinpoint when thousands of undated, hand-printed materials were created.
Hedges, who does field work in the Carribbean and happens to collect old maps of the area, conceived of the method after noticing that later editions of the same maps had more line breaks. The flaws exist because printmakers often used the same wood blocks and metal plates for decades and those components deteriorated over time. He started thinking that the flaws were analogous to the mutations that occur in genetic material. Such mutations do not happen at evenly spaced intervals, but if you can find a lot of them, you can come up with an average rate at which the mutations occur over time. It’s called a molecular clock technique. “I’m used to using molecular clocks and counting mutations in genes,” Hedges says. “I thought maybe the same principle might apply to this case with prints.”
More here.