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Re: [BKARTS] Dating prints: correlating age and wear



I thank Professor Terry Belanger for his critical comments. It is natural to
be skeptical about any new method and only time will tell how whether this
one is generally useful or not. However, he is incorrect about his major
point regarding copperplate wear (see below).

I encourage anyone interested to look at the scientific article describing
the method, for a complete description, rather than popular news articles
which may skim over the evidence. This web site has a PDF of the article:
http://evo.bio.psu.edu/printclock/

Copperplate Wear
I presented evidence that copperplate wear (narrowing of lines) came from
abrasion (polishing) of the plates to remove time-generated nicks and
corrosion and not from compression by the printing press as generally
assumed. Professor Belanger disagrees and supports the "universally held"
hypothesis of plate compression, causing an "ironing-out effect" that he
says will narrow the grooves/lines.  

But this is not what happens when metal is compressed.  Just like a ball of
pizza dough when rolled, it expands as it becomes flatter. For example, if a
copper penny is placed on a railroad track and is compressed by a train, it
becomes much wider than a normal penny (also, the same occurs if you strike
a penny with a large hammer).  It logically follows that any grooves in a
copperplate that is compressed will become wider, not narrower.

To prove this point I used a burin to engrave a grid of grooves in two small
copperplates. I compressed one and eroded the surface of the other. All
lines in the compressed plate became wider and all in the eroded plate
became thinner, as predicted (see graph:
http://evo.bio.psu.edu/printclock/#CopperplateTest). I also made precise
measurements of different editions of Renaissance prints showing that there
was no expansion of print dimensions and hence no measurable compression of
the copperplates by the rolling printing press (see article). Thus the
universal assumption of copperplate compression is rejected. 

Other comments:
Number of impressions: The total number of impressions made from a single
Renaissance copperplate during its lifetime was essentially unknown until
the study by Bowen and Imhoff (2005) revealed 18,257 impressions for one
plate from the Plantin Press. Previous estimates ranged from a few hundred
to a few thousand, but most of those were tied to limited print runs and
anecdotal comments, not actual documents from the press itself. Professor
Belanger is not persuaded that the larger number from Bowen and Imhoff is
representative, and favors the smaller numbers. But even if the larger
number proves to be an exception, it nonetheless shows that a copperplate
was capable of producing a very large number of impressions. In turns, this
adds support to the hypothesis that the printing press may not be the sole
or even major culprit in "wearing out" the plate. 

Print runs of books: here I think Professor Belanger misunderstood the
methods, because nothing in my study is "dangerous" (I hope!). For one of
several statistical tests - not a critical aspect of the study - I needed to
estimate the *relative* numbers of books from different editions, and did
this by consulting global catalog sources (WorldCat etc.) and contrasted
that by assuming a constant number per edition. *Absolute* numbers were not
needed, and if Professor Belanger can recommend a better method I am open to
suggestions.

Climate and storage conditions: Many factors will affect the deterioration
of both woodblocks and copperplates, and I noted these in the article. Too
little information is available yet to know how much variation exists. But
the method works by comparing prints from the *same* plate (usually same
printer and location), not from *different* plates or from different
printers, and thus Professor Belanger overstates the nature of the
variability.  He also includes "number of impressions" which was a factor
that I excluded with statistical tests.  
Blair Hedges
________________________
S. Blair Hedges, Ph.D.
Professor of Biology
Pennsylvania State University
208 Mueller Lab
University Park, PA  16802-5301 
tel. 814-865-9991
http://evo.bio.psu.edu/hedgeslab/

-----Original Message-----
From: Book_Arts-L [mailto:BOOK_ARTS-L@xxxxxxxxxxxxxxxx] On Behalf Of Terry
Belanger
Sent: Tuesday, July 11, 2006 2:03 PM
To: BOOK_ARTS-L@xxxxxxxxxxxxxxxx
Subject: [BKARTS] Dating prints: correlating age and wear

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