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Subject: Copper green pigments

Copper green pigments

From: Judy Bischoff <bischojj>
Date: Friday, February 2, 1996
In response to Tom Chase and Cor Knops, I have recently run across
one article of interest:

    Banik, G. 1989. Discoloration of Green Copper Pigments in
        Manuscripts and Works of Graphic Art. Restaurator. 10:61-73.

I believe that the chemistry of cellulose degradation in the
presence of Cu+2 and Cu+1 is fairly well established and can be
found in the very old chemistry literature.  Cu+2 is used to test
for reducing sugars, those carbohydrates which are easily oxidizable
(that is, bearing a terminal aldehyde group).  This aldehyde is
oxidized to the carboxylic group via the conversion of Cu+2 (blue)
to the Cu+1 (red) form and ultimately to elemental copper.

The buildup of acidic species, especially in the presence of any
moisture would favor acidic hydrolysis of cellulose in the areas of
this buildup, providing additional reducing sites for reaction with
the copper species.

This chemistry is the basis for analysis of reducing sugars and the
carbohydrate assay is called the "Fehling's Test".  and also the
basis for an old test of cellulose degradation called the "copper
number".  I checked some of my organic lab texts as well as some of
my biochemistry stuff for original references, but I think the
chemistry is so old, that it is buried in the ancient chemistry
literature, perhaps early 19th century.  A good place to start might
be "Chemical Abstracts" or "Tappi".  Hope this helps a little.

Judy Bischoff
Assistant Professor of Conservation Science
Buffalo State College
Art Conservation Department

                  Conservation DistList Instance 9:58
                 Distributed: Sunday, February 4, 1996
                        Message Id: cdl-9-58-003
Received on Friday, 2 February, 1996

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