Permanent colour change in cotton with use of low heat spatula

I recently worked on a double sided painted banner made of 2 pieces
of red cotton which were stitched together along all four sides. The
design was painted using oil paint, and due to the stiffness and
feel of the cotton ground fabric we presumed that some sort of
sizing might have been applied prior to the design being painted on.
The banner is not made by a known maker, so it was not possible to
look up documentation of how this particular banner maker worked.
According to our sources the banner was made c. 1925.

Part of the treatment we carried out was consolidation of some of
the painted motif using 2% Salianski isinglass.  The main components
of the painted design were the same on both sides of the banner but
they were not positioned exactly in the same position.  When we heat
reactivated the consolidated area of paint on the front face of the
banner at 65 deg. C the colour of the unpainted cotton of the
reverse face of the banner was observed to deepen slightly.

Because of the construction of the banner it was only possible to
gain access to the back of either face of the banner via a small
area of damage.  From what we could see through this hole the
painted motive had only partially penetrated through the fabric,
which seemed to imply that a sizing might have been added.

We were able to take a small sample of the cotton from the damaged
edge. Results of the FTIR analysis that we carried out showed the
main peaks to be cotton and the remaining peaks to probably be due
to accumulated dirt.  There is no paint this close to the edge so it
is possible that is no sizing at this point either.  The other test
methods I discussed with our Research Fellow in Conservation Science
had to be rejected as they would have been too intrusive. A painting
conservator colleague suggested that sizing could have been animal
glue or gelatine based but he was mystified to the deepening of the
colour.

I am very interested to know what is happening to this banner.  Has
anybody come across a similar problem and did you find out the
reason why it happened?

Anne Laila Kvitvang, Cand Mag, MA Tex Cons
Conservator
Textile Conservation Centre
Winchester School of Art
University of Southampton
+44 2380597100
Fax: +44 2380597101


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                  Conservation DistList Instance 22:5
                  Distributed: Thursday, July 17, 2008
                        Message Id: cdl-22-5-018
                                  ***