Painting damaged by bat excrement

I would highly appreciate any field report, links, recommendations
of literature, comments on animal excrements on easel paintings or
comparable.

In the present case, there's bats' excrement both on the painting's
(oil on canvas) rear side and front. Liquid from accumulated
excrement has penetrated from the rear side to the front side of the
painting and in consequence deteriorated the paint layer and caused
some white and crystalline blooming on the paint layer.

Does anybody have experience with treating that type of damages on
an oil painting? Can the constituents of excrement which have
migrated into the painting's structure cause further damage in case
of contact with water or high relative humidity? Can the painting
considered to be stable if displayed on a dry place? Is it necessary
to extract the excrement fully from the painting's structure?

Christina Spaarschuh, paintings conservator, Dipl.
Norwegian Institute for Cultural Heritage Research
P.O. 736 Sentrum
NO-0105 Oslo
+47 2335 5066


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                  Conservation DistList Instance 24:2
                  Distributed: Thursday, May 27, 2010
                        Message Id: cdl-24-2-020
                                  ***