Retouching

It's really great to see questions and debate arising from MPU, it
was after all one of the main aims of the conference--to bring these
issues into the spotlight and highlight the ongoing and increasing
need for collaborative research between paint manufacturers,
conservators and conservation scientists. I felt that the scientific
contributions to the conference offered an enormous amount of
information to the conservation profession, with an acknowledgement
that research in this field is still in its infancy and that the
application of this information to the complex practical problems
posed by works of art has to be a professional priority.

My photomicrographs of the surfaces of acrylic emulsion paints also
showed no evidence of damage to the surfaces of the pigmented
emulsion films I tested, until I started swabbing with acetone,
ethanol and xylene, which would be expected.  I had to move to
Atomic Force Microscopy to see any evidence for any change which
essentially consisted of the removal of the surfactant layer, which
we knew was happening with aqueous and polar systems from FTIR-ATR
analysis.  Mark is right in saying that the non-polar system I used
did not remove surface surfactant, and the physical testing I did
also showed that the changes in physical properties such as
stiffness were also minimal.

What I did find with mineral spirits--in agreement with the
Jablonksi et al. AIC publication--was that colour was more easily
removed, particularly with organic pigmented paints.  A simple test
where I put pieces of paint in water and in Stoddard solvent for 24
hours revealed that the Stoddard solvent had turned the colour of
the paint, but the water had not, which translated to more colour on
my swabs when I made the test more 'realistic'.  Gloss levels
treated with Stoddard solvent tended to vary little from the
controls, and although this solvent caused the greatest amount of
colour change, the actual amount was a maximum of +0.1 Delta E 94
units, which by all standards is negligible (I haven't yet looked at
the possible changes caused by multiple surface cleaning
treatments).  The only other thing I noticed was that there was a
very slight (0.1%) weight gain for samples that had been immersed in
Stoddard solvent for 1 hour, when all the aqueous systems caused
weight loss.

It was very encouraging to read that Golden MSA varnish is at least
in the short term, able to be removed, but this process needs to be
investigated with respect to the long-term properties of the varnish
and possible cumulative effects of multiple removal treatments on
the paint films.  I would think most practicing conservators would
agree, and I encourage conservators to participate by painting out
varnished paint samples using the methods Mark suggests, as well as
solo varnish layers on various substrates and leaving them to age
naturally, as we have done with many other materials. These samples,
(when well documented), can prove to be very useful to all of us.


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                  Conservation DistList Instance 20:1
                  Distributed: Saturday, June 24, 2006
                        Message Id: cdl-20-1-009
                                  ***