Dating Hidden Treasures

Reported November 2006

UNIVERSITY PARK, Pa. (Ivanhoe Broadcast News) -- Starry Night, Las Meninas and Mona Lisa. They are the work of masters, but when precisely were they created?

He's not the cracking the DaVinci Code or creating a stir on Antiques Road Show, but biologist Blair Hedges, Ph.D., is trying to answer this question.

Dr. Hedges, of Pennsylvania State University, found by studying different editions of the same print, he could pinpoint the date of previously undated works. He calls this the "print-clock" method.

"It measures the change in the wood and the metal used to make the prints," he tells Ivanhoe. Print experts often use a printer's watermark on the paper to place a date on previously undated works. Dr. Hedges says the watermark method is not as accurate as the print-clock method because it dates the paper, not the print.

Early craftsmen used hand-cranked printing presses, with the letters carved into wooden blocks or copperplates. To determine the date of old prints made from woodblocks, Dr. Hedges scans digital photos into this computer and uses a digital analysis software program to count the number of breaks in the lines.

For prints made with copperplates, he looks at the level of fading in the lines. With each edition of the same book or print, the ink appears lighter. A computer program counts the number of pixels from the scanned digital photo.

"Every different edition after the original one will have more and more white pixels," Dr. Hedges says. He found the changes in the prints were clock-like because the breaks in the wood, and thinning of the copper occurred evenly over time. "People want to know when things happened, for example, when a piece of art was created, when an idea was thought of. When a discovery was made."

The print-clock method may help historians fill in those blanks.

Click here to Go Inside This Science or contact:

Blair Hedges, Ph.D.
Biologist
Pennsylvania State University
(814) 865-9991
science@psu.edu

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