Cleaning copper intaglio plates

The library where I work has acquired a number of copper map
printing plates.  The plates are the official United States
Geological Survey plates used to print topographic maps in the late
1800s and early 1900s.They are smeared with what looks like ink I'm
guessing from their age that this would be petroleum-based printer's
ink.  We would like to clean the plates and prepare them for storage
and occasional exhibition.  I have a few questions:

What would you recommend (or *not* recommend) we use to remove the
ink, both from the surface of the plates and from the engraved
lines?

The plates I've seen displayed have a white substance in the lines.
It may be a residue from the cleaning, but it does make the engraved
lines easier to see.  What, if anything, could we use (or again,
what should we avoid using) to make the lines easier to see, once
the plates have been cleaned?

After the plates are cleaned, would you advise coating them with
anything to prevent oxidation of the copper?

We are thinking of storing the plates in individual custom sink mats
to protect them.  Opinions/alternative suggestions?

Thanks for your help,

Laurie Jedamus
Collection Management and Preservation
University of Minnesota Libraries


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                  Conservation DistList Instance 30:7
                  Distributed: Saturday, July 2, 2016
                        Message Id: cdl-30-7-020
                                  ***