The Print Clock (IMAGE) Penn State Caption The print clock. In these models, close-ups of a carved woodblock (above) and engraved copperplate (below) are shown, corresponding to a curved black line on the print behind it, at two time periods. Over time, cracks develop in the woodblock resulting in line breaks on prints. With copperplates, erosion of the surface produces thinner groves and thinner lines in prints. For both, the change is time-dependent. Credit Blair Hedges lab, Penn State Usage Restrictions Printed imges must be accompanied by the credit line: Blair Hedges lab, Penn State. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.