Retouching

Mark D. Gottsegen <mdgottsegen [at] earthlink__net> writes

>Andrea di Bagno <adibagno [at] mfah__org> writes
>
>>PVA or MSA paints as suggested by Mark Gottsegen are not a viable
>>choice if you wish for reversibility as the solvents needed to remove
>>them would damage the original paint layer.
>...
>
>One conservator touched on surface coatings and commented that
>varnishing was not an option.  Mark Golden and I later discussed this
>and wondered why?  The stronger solvents needed to remove a
>cross-linked coating from an oil painting are carefully monitored so as
>to avoid solubilizing the oil paint films; why could there not be the
>same theory applied to the cleaning of a varnished acrylic dispersion
>painting?  It has been amply demonstrated that acrylic dispersion paint
>films are easily penetrated by dirt and moisture and are therefore
>especially difficult to clean.  Wouldn't giving them a "protective"
>coating make the cleaning easier, as long as the solvents and solvent
>checks were closely controlled.  I'd like to see comments on this--they
>would be of help to me and manufacturers like Golden in making
>recommendations to artists.

I'll attempt to put this issue in a nutshell from the point of view
of a bench conservator.

Oil paint chemically hardens with age.  In general, as it grows
older it becomes less soluble to solvents.  An oil painting that is
10 years old is still soluble/sensitive to naphtha, while a 100 year
old oil painting is rarely sensitive to naphtha or stronger solvents
such as xylene, toluene, or even mixtures containing acetone.
Varnishes are more soluble than aged oil paint, particularly some of
the new synthetic varnishes that indefinitely remain soluble in mild
solvents.  If there are not complicating factors, such as varnish
incorporated into the paint itself, varnishes can safely be removed
without damaging the paint.

Acrylic paint does not become harder with age.  Once it has gone
through its varied drying processes it may no longer be soluble in
water, but it remains soluble in very weak organic solvents such as
naphtha or mineral spirits.  The oldest acrylic emulsion paintings
at this point are approximately 30 years old.  They are still
sensitive to mild organic solvents, and many are sensitive to water
as well.  There are no varnishes currently available that have a
lower solubility than acrylic emulsion paint, particularly after a
relatively short period of aging (many varnishes become at least
slightly less soluble with age). Therefore there is no separation
between the solubility of the acrylic paint and any available
varnish.  There is no margin of safety that allows the removal of a
varnish layer.

In considering this one question comes to my mind.  From a
conservation stand point the emphasis has long been on finding a
varnish with the lowest possible solubility that also has useful
optical and handling qualities.  We may have reached the limits in
that search.  From a paint manufacturing standpoint, would it be
more fruitful to explore acrylic paint formulations that are
slightly less soluble, which could then safely be coated with the
existing varnishes?

Perry Hurt
Conservator for Regional Conservation Services
North Carolina Museum of Art
Direct phone: 919-664-6813
Museum phone: 919-839-6262
Fax: 919-733-8034


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                  Conservation DistList Instance 19:60
                  Distributed: Thursday, June 15, 2006
                       Message Id: cdl-19-60-003
                                  ***