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Smithsonian American Art Museum Lunder Conservation Center
Analytical Test Results and Treatment Report
Artist: Tom Wesselmann
Title: Still Life #12
Accession #: 1986.23
Date: 1962
Materials: oil and acrylic paints, fabric, paper,
metal, photomechanical images
printed on paper, fiberboard
Dimensions: 48 x 48 x 3/8 in. (122 x 122 x 1 cm)
Requested By: Ann Creager, Paintings Conservator
Examiner: Sharra Grow, Graduate Intern
Supervisor: Ann Creager, Head of Conservation at
SAAM; Amber Kerr-Allison, Kress
Fellow
Contributors: Sharra Grow, Graduate Intern
(SAAM); Jia-Sun Tsang, Senior
Paintings Conservator (MCI); Rebecca
Gieseking, Paintings Conservation
Intern (MCI); Nicole Little,
Conservation Scientist (MCI);
Suzanne Lomax, Senior Scientist (NGA); Melvin Wachowiak,
Senior
Conservator (MCI); and Judy Watson, Conservation Scientist
(MCI)
Report Date: August 1, 2008
Analytical Test Results Polarized Light Microscopy
The colorant in the red paint sample appears to be a lake
pigment. A McCrone pigment sample
set was used for comparison. No more conclusive results could be
made using polarized light
microscopy.
Cross-sectional Microscopy
This cross section was taken from Sample 2 (see fig.20). The
paint layering on the red of the
table cloth shows white layers under the top red paint layer and
cellulosic fibers below the white
layers (see figs. 11, 12). Three distinct white layers can be
seen underneath the red paint layer
when the sample is viewed under ultraviolet (UV) light (see fig.
13). The presence of the
cellulose fibers underneath the lowest white layer confirms that
this is the ground or priming
layer on the fiberboard support. The ground contains large and
coarse particles in comparison
with the two white layers and red layer above, which contain
very small and evenly ground
pigments.
Figure 1: Still Life #12, normal light,
before treatment
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Scanning Electron Microscopy – Energy Dispersive Spectroscopy
(SEM-EDS)
This analysis negates the hypothesis that the red paint
contained cadmium-based pigments, as no
cadmium was detected. In fact, there were no heavy elements
found in the red paint layer except
for chlorine which is likely an artifact of the embedding
materials (see figs. 18, 19). It is believed
that the red paint layer contains an organic dye or lake
pigment, though the presence of chlorine
is not yet understood. The presence of silicon in the ground
layer may suggest glass or sand as a
coarse filler (see figs. 14,15). Calcium is also found in the
ground layer, which could be from
calcium carbonate, often found in ground and priming layers (see
fig. 17). A significant amount
of titanium was detected in all three white layers suggesting
that titanium white is a pigment in
these paints (see fig. 16).
Fourier Transfer Infrared- Attenuated Total Reflection
Spectroscopy (FTIR-ATR)
FTIR-ATR spectrum was obtained from efflorescence taken from
Sample 3 and the surrounding
area (see fig. 20). After comparison with known spectra, the
spectrum from the efflorescence
sample indicates the presence of free fatty acids, likely
palmitic acid or stearic acid. The two
sharp peaks at 2850 cm-1
and 2920 cm-1
indicate straight hydrocarbon chains like those in fatty
acids. The peak at 1700 cm-1
indicates carbon-oxygen double bonds and the broad peak
between
2500-3500 cm-1
is caused by oxygen-hydrogen bonds, indicating the presence of
carboxylic acid
groups which are found on fatty acids.
FTIR spectra were also obtained for the ground and the white and
red layers used to paint the
tablecloth (see fig 21, 22). The ground appears to be acrylic,
and both paint layers appear to be
oil. The spectra of oil-based and acrylic-based paints differ
significantly in the carbon-hydrogen
region just below 3000 cm-1
. While oil paints have two distinct peaks in this region
(indicating
the long hydrocarbon chains in the oils), acrylic paints have a
single broad peak caused by the
overlap of several smaller peaks.
X-Ray Diffraction (XRD)
XRD performed on efflorescence resulted in spectra indicating
the presence of n-paraffin
primarily, with trace amounts of two forms of palmitic acid
(Perhydrotriphenylene palmitic acid
and α-palmitic acid) (see fig. 23). Although initial examination
of the XRD spectra indicated the
presence of lead silicate, the lack of any other lead or
silicate peaks does not support this
possibility. Stearic acid was not found in the sample,
indicating that palmitic acid is the only
fatty acid present.
Gass Chromatography/Mass Spectroscopy (GC/MS)
GC/MS performed on a sample of the efflorescence resulted in a
spectrum which included
primary peaks from methyl palmitate and methyl stearate, with a
P/S ration of 4.40 (see fig. 24).
Small amounts of C-14, C-15, C-17 and C-20 fatty acids were also
found to be presence. It is not
possible from these results to determine whether the initial
species were fatty acid salts or free
fatty acids.
Samples Taken
Sample 1: Red paint from painted fabric at lower PR corner
Sample 2: Red paint from checkered tablecloth taken from lower
edge
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Sample 3: Efflorescence crystals taken from the red paint of the
checkered tablecloth at lower
edge
Sample 4: Red paint from the vertical collage strip on the PR
edge
Sample 5: Coated paper from the upper PR corner
Sample 6: Red paint from the top edge of the red apple
Sample 7: Red paint pigment from checkered tablecloth taken from
PR lower edge (see fig. 11)
Sample 8: Fiberboard from the lower PL corner
Sample 9: Efflorescence crystals taken from red paint of the
checkered table cloth near the lower
edge (taken at Jia-Sun Tsang’s request)
Sample 10: White paint on the checkered table cloth near the
lower PR edge (taken at Jia-Sun
Tsang’s request)
Sample 11: Ground layer taken from the lower edge (taken at
Jia-Sun Tsang’s request)
Conclusions and Further Research The red paint is most likely an
organic lake pigment and the three white layers beneath it
contain
a significant amount of titanium white. The red paint layer and
the white paint layer immediately
beneath are oil based and the ground is acrylic based.
Results from FTIR-ATR, XRD, and GC-MS confirm the presence of
free palmitic acid as a
major component and paraffin as a minor component. The
observation that this fatty acid is able
to form solid crystals on the painting further supports that it
is likely palmitic acid, being a
saturated fatty acid. Unsaturated fatty acids, such as oleic
acid, tend to be liquid at room
temperature and therefore would not form solid crystals on a
painting in a museum environment.
Additionally, unsaturated fatty acids tend to crosslink with
each other, while saturated fatty acids
are unable to crosslink because of their lack of carbon-carbon
double bonds, making the
saturated fatty acids more likely to migrate to the surface of
the painting.
One important question remaining is what instigated the
migration of the fatty acids and surface
crystal formation? It could have to do with polymorphic
transformations these compounds are
able to make. Polymorphism is the occurrence of several
different crystal forms from the same
chemical compound. For example, calcium carbonate is dimorphous
(having two possible crystal
forms), crystallizing as calcite or aragonite. Saturated
triglycerides, which may be found in low
quality or slow drying oil paints that Wesselmann may have used,
can transform and assume
three different crystals – alpha, beta prime, and beta.
It appears that the beta form of the crystal best matches the
visual observation of the white
crystals found on the Wesselmann painting; long, opaque, white
needle crystals. This crystal
form results from the slow cooling of the oils. This process of
slow cooling oils, often called
winterizing, has been used by the food industry and candle
manufacturing to remove traces of
wax and higher melting glycerides from vegetable oils. In this
process waxes can generally be
removed by chilling and filtering. Separation of high-melting
glycerides, or stearine, usually
requires very slow cooling in order to form crystals that are
large enough to be removed by
filtration or centrifuging. It is possible that non-drying oils
present in the Wesselmann painting
underwent a kind of winterization through very slow cooling that
resulted in the efflorescence
formation on the painting surface. This slow cooling may have
occurred during the
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environmental change of the painting when it was removed from
sto1rage and placed in the
newly renovated gallery space in the museum.
This painting has been and will again be glazed with Plexiglas,
so another important question to
consider is whether or not the framing and glazing has an effect
on the formation of
efflorescence on the paint surface. If it does exacerbate the
problem, what is an acceptable
alternative framing and glazing? Tests further exploring the
influence of environmental change
on the formation of fatty acid efflorescence on paintings have
also been suggested. Research to
date on the formation of efflorescence has given us a clearer
understanding of the composition of
these crystals. However, the crucial issue of prevention still
requires further research, which
would benefit not only this painting, but the many paintings,
objects and other artworks which
suffer from similar surface formations.
Treatment
1. Documented the condition of the artwork before treatment in
written and photographic form
(see figs. 2, 3, 6, 8).
2. Re-adhered loose edge of the ‘ham’ paper collage element
using Beva 371, first confirming
the insolubility of the red paint layer in petroleum benzine
(see figs. 8, 9).
3. Removed the surface efflorescence using the CO2 snow gun
after testing (see figs. 4, 5, 10).
Because of the ease of removal no other techniques were required
to clear the efflorescence from
the paint surface. Visual and microscopic examination of the
paint surface upon removal of these
crystals showed no degradation or change to the original paint
surface. (I will probably add a
more detailed explanation of the CO2 snow gun)
4. Documented the artwork after treatment in written and
photographic form.
1 Joyce Hill Stoner told me of a discussion she had with Steve
Kornhauser at the Wadsworth Atheneum; three
temperas on panel by Andrew Wyeth in the Wadsworth collection
are all housed differently (one has no glazing, one
is glazed with glass, and one is in a climate-controlled box),
but all three have developed efflorescence.
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Figures
Figure 2: Still Life #12, normal light, before treatment
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Figure 3: Still Life #12, raking light, before treatment
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Figure 4: Still Life #12, normal light, after treatment
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Figure 5: Still Life #12, raking light, after treatment
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Figure 6: Still Life #12, detail, raking light, BT Figure 7:
Still Life #12, detail, raking light, AT
Figure 8: Still Life #12, detail, BT Figure 9: Still Life #12,
detail, AT
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Figure 10: Still Life #12, CO2 snow gun used for efflorescence
removal, DT
Figure 11: Sample 2 cross section, dark field and transmitted
light
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Figure 12: Sample 2 cross section, transmitted light
Figure 13: Sample 2 cross section, UV light
Figure 14: Sample 2, SEM image Figure 15: Sample 2, SEM-EDS,
silicon
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Figure 16: Sample 2, SEM-EDS, titanium Figure 17: Sample 2,
SEM-EDS, calcium
Figure 18: Sample 2, SEM image Figure 19: Sample 2, SEM-EDS,
chlorine
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Figure 20: FTIR Spectra of the efflorescence from Sample 3 and
known palmitic acid and
stearic acid spectra for comparison
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Figure 21: FTIR spectra of the ground from Sample 11
Figure 22: FTIR spectra of the ground from Samples 6 and 10
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Fig 23: XRD Spectra of efflorescence and known spectra for
paraffin and two palmitic acids for
comparison
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Figure 24: GC/MS spectrum of the efflorescence
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Figure 20: Still Life #12, sample locations for technical
analysis
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Bibliography
Boon, J. J., P. Noble. 2007. Metal soap Degradation of Oil
Paintings: Aggregates, Increased
Transparency and Efflorescence. Paintings conservation catalog
Vol. 19, American Institute for
conservation Paintings Specialty Group. Washington, D.C.:
AIC.
Eccher, D. 2005. Tom Wesselmann. Rome, Italy: Museo d’Arte
Contemporanea Roma.
Garver, T.H. 1971. Tom Wesselmann: Early Still Lifes: 1962-1964.
Kansas City, Missouri:
Nelson Gallery-Atkins Museum.
Glenn, C. 1974. Tom Wesselmann: The Early Years: Collages
1959-1962. Long Beach,
California: The Art Galleries, Californian State University.
Hunter, S. 1994. Tom Wesselmann. New York, New York: Rizzoli
International Publications,
Inc.
Loon, A. v. 2008. Color Changes and Chemical Reactivity in
Seventeenth-Century Oil Paintings.
Amsterdam, The Netherlands: FOM Institute for Atomic and
Molecular Physics (AMOLF),
Molecular Paintings Research Group.
McCrone, W.C. and J.G. Delly. 1973. The Particle Atlas: Edition
Two. Ann Arbor, Michigan:
Ann Arbor Science Publishers, Inc.
Ordonez, E., J. Twilley. 1998. Efflorescence on Works of Art.
WAAC Newsletter 20 (1).
Schilling M. R., S. Lake, E. Steele, and S. Q. Lomax. 2002.
Modern Science and Contemporary
Paintings: Preserving an Evolving Legacy. Conservation: The GCI
Newsletter 17 (3): 4-10.
Stoner, J. H. 2008. Personal communication. Lunder Conservation
Center, Smithsonian
American Art Museum, Washington D.C.
*Select text, data, and images were taken from Smithsonian
Museum Conservation Institute
Technical Report MCI 6213 Still Life #12 by Tom Wesselmann,
Smithsonian American Art
Museum, compiled and written by Jia-Sun Tsang, in order to
complete this report.