Print Clock

The “Print Clock” is a system of dating prints developed by S. Blair Hedges, Professor of Biology at Penn State. The method depends on the supposition that printing surfaces deteriorated at a clock-like rate.

The print clock is a method for dating undated books and prints that were produced by hand-operated presses, thus since the 15th Century. It is based on the hypothesis, backed by observations, that woodblocks and metal plates (e.g., copperplates) deteriorated in a clock-like manner during their lifespan, which was often decades… By measuring this change across different editions of the same print, and calibrating the rate with dated editions, it is possible to estimate the age of the undated work.

From a printmaker’s perspective, the most interesting thing about this (aside from these sweet diagrams) is the conclusions Hedges has drawn about how printing matrices become worn.

Aging of the wood creates breaks in the relief of a carved woodblock, causing line breaks on the resulting print. For copperplates, the image fading I measured is the result of the thinning of the etched and engraved lines caused by the erosion of the copper surface, which results from the steady corrosive effects of acid in the atmosphere plus the periodic removal of the accumulated corrosion by scouring and polishing of the plates prior to each print run… The assumption in published papers in this field was that prints from later editions of the same copperplate are paler because the enormous pressures in the printing process were flattening the copperplate, but my laboratory studies proved that this is not the case.

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Categories: Resources, Technology

3 Responses to “Print Clock”

  1. kvh says:

    Hogwash I say.

    Perhaps 40th edition…

  2. Luther says:

    When this was originally written about in the NY Times (I think) I wrote an email to Professor Hedges. As a printer I know that there are too many variables to make an accurate clock as far as the plate goes. His theory does not really take into account that two prints made right after each other can be drastically different. Pressure, the amount of wiping and paper wetness could all give false readings. He did write back to me telling me that I didn’t know what I was talking about which made me write back to him telling him that he didn’t know what he was talking about. Fun stuff.

  3. Blair Hedges says:

    Hi Luther,
    I remember our email exchange from 4 years ago and I just looked at it again. It was not at all how you characterized it. It was completely pleasant and informative. I ended with “This email exchange has been quite educational for me and I appreciate your time in explaining to me these details.” and you ended with “This correspondence has been the highlight of my day.”

    About your more recent comment regarding differences between two consecutive prints: It is true that individual prints can vary greatly for many reasons, and that is evident in the graphs that I showed in the original paper and a subsequent one (posted on That is why I used more than one or two prints in those analyses, to accommodate individual variation. Similarly, individual isotopic decays vary greatly but large numbers of them produce accurate geologic clocks.