Copper in starch paste

Silvia Oliveira Sequeira <s.o.sequeira [at] gmail__com> writes

>In the literature we have not found any information about the
>combination of starch paste with copper. We thought maybe it was
>some insecticide or fungicide compound added to this bio-susceptible
>glue, but there is nothing on this subject in the articles we have
>found. Does anyone know anything about this starch paste/copper
>combination?

I too have come across copper salts added to paste.  In my case it
was 19th century paste on a British watercolour.  The first
indication of the presence of copper was the formation of a pink
deposit of metallic copper on my blunt scalpel blade while I was
scraping some of the softened paste away. Like you, I thought it may
have been added as a fungicide.  At the time I did manage to find a
19th century paste recipe that mentioned adding a copper compound to
the paste but cannot at present find my note of the source.

Coincidentally we are currently conserving a drawing with iron ions
in the paste (confirmed by potassium ferrocyanide/HCl spot test).

Nicholas Burnett
Director
Museum Conservation Services Ltd


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                  Conservation DistList Instance 21:37
                  Distributed: Friday, January 4, 2008
                       Message Id: cdl-21-37-005
                                  ***