Printing flaws reveal the age of historic documents

HISTORIANS have a new way to determine the age of books and engravings. The same wooden or metal blocks were sometimes used for many years to produce copies of documents or prints. Over that time, the flaws that developed in these blocks got worse, and these show up on the printed page. Evolutionary biologist Blair Hedges of Pennsylvania State University at University Park realised that these flaws could be used to date printed material. He took high-resolution scans of versions of the same prints made at different times and used imaging software to detect the flaws. For documents printed from…