Lead corrosion

Susan White <smwhitewhite [at] netscape__net> writes

>I'm currently working on a large wall relief (8x10 feet) by Robert
>Morris. The piece is constructed of sheet lead over a substructure
>of steel and particle board. It has been in a closed plywood
>container with white styrofoam for the past twenty years and is now
>covered in a tenacious layer of white corrosion (lead formate I
>think). Initial tests show the corrosion to be only very slightly
>soluble in concentrated acids (sulfuric and hydrochloric) and
>completely insoluble in most everything else (including hot water
>and sodium EDTA poultices).
>...
>...  Has anyone tried ion exchange resins on
>lead corrosion? Are they effective? ...

I have used ion exchange resins to treat lead corrosion on
archaeological objects with good results.  Generally, with those
objects the corrosion is holding the remaining metal together, so
the method does have to be used with some caution.  The challenge
that you will have in this particular case is creating a structure
to hold the resin and hot water in contact with the relief surface
without affecting the support.

The usual method is to immerse the entire object in the exchange
resin.  I have always followed the venerable method in Plenderleith
and Werner, 2nd Edition, 1971, The Conservation Of Antiquities and
Works of Art, pages 270-272.  I use Amberlite IR-120, a strongly
acidic, sulfonated polystyrene type cation exchange resin
(Mallinckrodt Inc.), but you might want to check on other types that
might be more specific for formates.

Not to second guess here, but was the relief checked for any type of
coating?  Even though it has corroded, there could still be a
coating on the surface that would make cleaning with something like
an aqueous chelate solution difficult.  Formaldehyde vapors would
easily penetrate through a polymer, such as shellac or a varnish,
that was not intended to serve as a barrier or sealer. You might
want to confirm that, if you haven't already, before proceeding with
any other methods.

Paul S. Storch
Senior Objects Conservator
Daniels Objects Conservation Laboratory (DOCL)
B-109.1, Minnesota History Center
345 Kellogg Blvd. West
St. Paul, MN  55102-1906
651-297-5774
Fax: 651-297-2967


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                  Conservation DistList Instance 17:58
                   Distributed: Monday, March 8, 2004
                       Message Id: cdl-17-58-004
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