November 1, 2006 A biologist developed a method to determine the date of antique prints made from hand-cranked presses. In his so-called print-clock method, image analysis software counts the number of breaks in the lines appearing in each print. Successive prints made from the same wooden or copper block show more breaks, since breaks in the wood and thinning of the copper occur evenly over time.
BACKGROUND: A biologist at Penn State University has developed a new and simpler method for discovering the date when centuries-old art prints and books were produced. The method could reveal long-sought information about thousands of undated works printed on hand-operated presses prior to the development of modern printing methods in the mid-19th century, including works by Rembrandt and Shakespeare.
THE DATING GAME: Dating manuscripts is traditionally a tricky business; antiquarians rely on analyzing fonts, type of paper, or printer's watermarks, among other features. The problem with such an approach is that it is highly personal. Hedges' new "print-clock" technique is similar to the molecular clock techniques used to time genetic mutations over several generations. He also uses this tool for finding the age of genetic material in his biological research. In the case of book dating, he measured time-related changes (deterioration) in over 2,500 works from the Renaissance, figuring that the changes were simply random errors in the printing devices, akin to the random errors in DNA that give rise to genetic mutation. First, he took digital photographs of the texts or prints to be studied. Then he used image-analysis software and standard statistical methodology to analyze those images. The software specifically detects and counts breaks in the lines of woodblock prints, and can measure fading of the etched and engraved lines of copperplate prints
SETTING THE TIME: To calibrate his "print clock," Hedges relied on the fact that the engraved wood blocks and copperplates used for printmaking deteriorate at a clock-like, constant rate over time, no matter how many books are printed at a time. The changes in print quality are caused when the wood and copper plates age during storage between print runs. He found that the number of breaks in the lines of images printed from woodblock carvings increased over time, while the image intensity became more pale in copperplate prints. (A line break is a faded line in a drawing that may have been bolder in an earlier edition of the same text.) Hedges studied images with known print dates made with the same woodblock or copperplate; this gave him a reference point for determining how the line breaks and other print features deteriorated over time.