Metal printing plates

Eric Alstrom <eric.c.alstrom [at] dartmouth__edu> writes

>The plates, which could be zinc (but I'm not positive) are covered
>by a white substance, which originally was thought to be mold.  I
>don't think it is mold, but rather some oxidation on the surface.  I
>am not a metals conservator, but was asked to experiment with one of
>the less interesting plates.  I tried washing in DI water and
>lightly scrubbing the surface.  The white substance seemed to
>disappear while wet but reappeared just as much as before when it
>dried.

I am not a chemist, but a printer.  About thirty five years ago (and
then for about ten years after that) I could get zinc plates made
for my letterpress printing.  They were strong and long-lasting. But
they gave off some poison of some kind in their manufacture, so they
were banned in California.  I had to use magnesium plates, which
work just fine, but they corrode (with a whitish "powdery" material
forming on the corroded surface).  The corrosion doesn't turn up for
many years.  I have recently checked some of my old plates, and the
magnesium ones are indeed in poor shape.  I have some considerably
older that are in excellent condition, and I think they are zinc.

Sid Berger
Simmons College
617-521-2228


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                  Conservation DistList Instance 17:33
                 Distributed: Tuesday, October 7, 2003
                       Message Id: cdl-17-33-002
                                  ***