Audobon lithograph

I have a Audubon lithograph depicting the American Red Fox,
dimensions 21.5 x 27.5 inches, dated 1846.  The client brought it to
me because of acidic degradation products around the perimeter of
the piece from a previous mat window, and a large discoloration on
one side of the print.  The large discoloration appeared to be a
large tideline.  When examined under longwave UV light, the area did
not fluoresce, but darkened to a deep purple.  I took the darkening
to be an indicator of alkaline metals from the water that had
previously damaged the print (the water in Nebraska is extremely
alkaline--close to pH 9 straight from the tap).

I have washed the print in deionized water (1:1 ethanol:DI water to
wet the print up first), in baths of gradual pH levels, using
calcium hydroxide to increase the pH level of the water baths.  I
then used a .1% solution (w/v) of sodium borohydride on the suction
table, followed by rinsing in calcified water.  When the
discoloration and the acidic degradation products were not reduced
sufficiently, I tried a .5% solution instead. The acidic degradation
product discoloration was reduced significantly while the discolored
"tideline" area was not. Longwave UV light examination revealed that
the dark purple regions were still present in those areas.

I am considering chelating agents, but of course, I don't know 1) if
it is a metal substance, 2) even if it is a metallic substance,
which metal it is, and 3) if chelating agents will harm the matrix
of the paper when applied to a large area. I am thinking more
sophisticated analysis might be necessary in order to determine what
is causing the problem, but I thought I would ask the conservation
community first to see if anyone had seen something similar to this
in a paper treatment and if so, what caused it and what was done to
remedy the problem. Many thanks in advance,

Tara Kennedy
Tara D. Kennedy
Paper Conservator
Gerald R. Ford Conservation Center
Nebraska State Historical Society
1326 S. 32nd Street
Omaha, NE 68105
402-595-1180
Fax: 402-595-1178


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                  Conservation DistList Instance 18:14
                 Distributed: Sunday, September 5, 2004
                       Message Id: cdl-18-14-025
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