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Subject: Weeping oil paint

Weeping oil paint

From: Niccolo Caldararo <caldararo<-a>
Date: Tuesday, December 18, 2007
Jenny Schulz <jennyal [at] gmx__li> writes

>Contemporary paintings in danger. I am working on a painting by Otto
>Piene from 1993 where white oil paint became liquid within a few
>months and has created sticky drips up to 20cm long. ...

I have seen this condition several times over the past 40 years.
Most recently in 2000 we examined a number of paintings by Gordon
Onslow-Ford that had been painted in the 1970s.  Mr. Onslow-Ford had
used a paint manufactured specially for his use by a man named Parls
with the help of a chemist, a Mr. Manheart. We traced some aspects
of their formulation to paints by Bocour, Aquatec and Poltice by
Gutierrez but other varieties seem to have been produced by artists
or specialist manufacturers after Liquitex's qualities.

Some information on this is in Robert Lodge's excellent article in
the AIC Preprints in 1988. Bocour's paints were based on Acryloid
F-10 called Magna and date from 1949; they vary in stability as we
see them today because many artists followed Bocour's advice and
added oil paint to them.  Linseed oil often separates over time
forming a very sticky layer on top.

After 1960 Bocour added more stabilizer (bleached beeswax) to
promote a paint that did not need the addition of oil paint and yet
could be applied like oils. In our samples from Onslow-Ford's work,
however, we found the surface displayed a coating of polyethylene
glycol (PEG) which had acted as a plasticizer in the special
Parls/Manhardt formula.  The rest of the test results indicated a
alkyd resin paint.  Since alkyd resins are a condensation polymer of
glycol and phthalic anhydride, it seems the migration makes sense,
though we did have samples that had never been exposed to light,
heat or moisture from his studio that had not evidence of migration.

Alkyd resin paints were available from GE after 1914 and were used
by people like Frank Sterner, WPA artists like Rockwell Kent and
later by Jackson Pollock. Unfortunately, our artificial aging tests
of sample canvas with pigment from the 1970s and pigment samples
drawn from paint cans did not demonstrate similar vectors of
degradation which may indicate that aging factors are significant
but not intrinsic.

We could not find a solubility parameter that removed the migration
product without also removing surface pigment. In consultation with
Dr. John Asmus we decided that the safest modality was to use laser
cleaning.  I hope this helps,

Niccolo Caldararo, Ph.D.
Director and Chief Conservator
Conservation Art Service

                  Conservation DistList Instance 21:37
                  Distributed: Friday, January 4, 2008
                       Message Id: cdl-21-37-006
Received on Tuesday, 18 December, 2007

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