Metal soap aggregates in oil paintings

Some of you may have seen a questionnaire that was sent out attached
to The International Council of Museums - Committee for Conservation
(ICOM-CC) Paintings Group Newsletter (August 2002) regarding the
occurrence of metal soap aggregates in oil paintings. Although we
have had many responses, with examples of these so-called
protrusions and inclusions in paintings ranging from the 15th
century to the 20th century (both canvas and panel paintings), in
talking to conservators we have the feeling there are many more
cases out there.

So far aggregation is only observed associated with lead and zinc
based paints. Protrusions are a more threatening class of metal soap
aggregates because they disturb or break through the paint surface
and even through the varnish causing paint loss, after undergoing
dramatic volume changes. We have many examples of 17th century
paintings where extensive pin-point paint losses can be attributed
to protruding lumps of lead soaps. Probably the most extreme case is
a Van Gogh painting where protruding zinc soaps, which are still
active, have severely embrittled the paint.

If anyone comes across examples, I can send them a questionnaire via
email, or post. The questionnaire also contains references for
articles already published on this phenomenon. The function of the
questionnaire is to better gauge the extent and diversity of this
deterioration phenomenon. The project is headed by Prof. Dr. Jaap
Boon at the research Institute, FOM-AMOLF in Amsterdam. I
participate in this project by documenting examples in paintings and
as a liaison between scientists and collections.

Petria Noble
Senior Paintings Conservator
Royal Cabinet of Paintings Mauritshuis
The Hague, The Netherlands
+31 70 3023463
Fax: +31 70 3653819


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                  Conservation DistList Instance 16:62
                 Distributed: Thursday, April 17, 2003
                       Message Id: cdl-16-62-005
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