Consolidation of gouache

At one time I worked on a number of watercolor paintings on silk.  The
watercolor pigments were very coarsely ground and had very little
apparent binder.  They were to be stabilized in preparation for washing
to remove accumulated grime, bird and rodent droppings, and other
horrors acquired while stored for many years surface-up in an old
warehouse.

I used two applications of 1% polyvinyl butyral (Butvar B-98, I think)
in ethyl alcohol.  These were flooded on the painted areas with a
disposable polyethylene pipet.  This material is soluble in ethyl
alcohol,  but it does not readily form discrete films from ethyl alcohol
solutions.  The resin "agglutinates" or collects between the pigment
particles, binding them together.  The lack of saturation by the resin
matrix avoids color saturation effects or shininess. The binding
geometry can be clearly seen under a microscope.  Since the resin will
form bound chains of pigment-soluble dirt-pigment, when the dirt is
washed out, the consolidation must be repeated or renewed.  It still
remains invisible, however.  A caution--under certain conditions, the
resin will reticulate, creating a blanched appearance.  Not to worry, as
rewetting with ethyl alcohol will usually remove the "blanching".

Some people have indicated concerns, mostly theoretical, that this class
of resins may not be stable over long periods.  I have used the stuff
for over 20 years, as have many textile conservator colleagues, and have
yet to see or hear about any shift in appearance or resolubility.

Good luck.

Geoffrey I. Brown
Kelsey Museum, University of Michigan

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                  Conservation DistList Instance 7:82
                   Distributed: Monday, May 16, 1994
                        Message Id: cdl-7-82-001
                                  ***