New Insights into the Cleaning of Paintings

136 • smithsonian contributions to museum conservation
In order to ensure reproducibility and accuracy in the cleaning
operation, mock- ups were immersed in the cleaning solution
and tests were run in duplicate. As previous reports show that
most of the material lixiviated from a paint sample occurs in the
first few minutes (Ormsby and Learner, 2009), the effect of a fiveminute
immersion was evaluated.
The effects of cleaning (both efficacy of dirt removal and
changes to the paint film) were assessed by the following: level
of dirt removal, color change, loss of extractable material, detection
of residues, and disruption to the paint surface. Changes
to the paint surface morphology were monitored by atomic
force microscopy (AFM) in vibrating mode on areas of 50 × 50,
10 × 10 and 2 × 2 mm 2 . Alterations in the surfaces’ chemical
composition were assessed by Fourier transform infrared spectroscopy
attenuated total reflectance (ATR), and color coordinates
were collected with a portable colorimeter, using the CIE
L*a*b* system. Roughness values R a
obtained with AFM were
calculated on the 10 × 10 mm 2 scan areas, as an average of five
selected 2 × 2 mm 2 areas. The value presented is the average of
the two replicates.
RESULTS AND DISCUSSION
Artificial aging studies indicate that loss of paint plasticizer,
diisobutyl phthalate (DiBP), is the major alteration between
aged and unaged samples (Ferreira et al., 2010). The ATR spectra
from the artificially aged control sample showed no significant
signs of a surface enrichment with DiBP. Therefore, it was
expected that immersion could only remove negligible quantities
of plasticizer still present on the tests films. As expected,
only minor changes were seen in ATR spectra that can be tentatively
correlated to the extraction of this additive (Figure 1).
Moreover, DiBP was not detected among the residues remaining
after immersion.
Because of the irregular surface topography and affinity for
dirt that is retained by the paint surface, immersion of the samples
was not efficient for dirt removal. This was confirmed both
by optical microscopy and colorimetry.
Smaller AFM scan areas were found to be the most useful
because of the heterogeneous nature of the paint surface and
the technical difficulties encountered when scanning large features
deposited on the samples. Moreover, with the 10 × 10 and
2 × 2 mm 2 areas changes in the latex surface can be seen with high
detail (Figure 2). Pure water did not induce relevant alterations
on the morphology of the white paint. However, with the aqueous
solution of Brij700S the smoothness of the latex particles is
lost, and the polymer surface displays a more irregular texture,
which could be the result of surfactant residues left on the paint.
Large and protruding features appeared on the paint’s surface
after white spirit immersion.
Cleaning with an eraser resulted in both particles and/or
eraser additives being left on the surface. These residues could
not be identified with ATR, probably because of their small
FIGURE 1. The ATR infrared spectra. (top) Artificial aging of the
sample induces loss of the plasticizer, as seen from comparison of the
circled peaks. (bottom) The aged control sample shows no plasticizer
enrichment on the surface, and therefore only minor differences can
be observed in those peaks after water immersion.
quantity, but they are clearly related to the eraser because the
pattern left in the polymer surface is similar to that observed
when using it directly on mica sheets. Moreover, the physical
abrasion provoked by the mechanical action can account for the
decrease in the surface roughness.
CONCLUSIONS
These preliminary results offer a first insight into the response
of PVAc emulsion paints to cleaning procedures. Surface
roughness was not significantly affected with the immersion of
the samples in any of the tested solvents. However, changes in
surface morphology were observed for the surfactant solution
and even more for the white spirit. Immersion of the samples
was insufficient to obtain dirt removal. Moreover, surfactant residues
were not effectively removed. The most significant changes
were introduced by the eraser. Concern should be raised about
using Akapad for dirt removal in Sarmento’s White Paintings
as these paints might be liable to mechanical damage. Physical
disruption of the latex paint was only detected at the nanoscale;
however, it could result in a flattening of the paint surface that is
contrary to the distinctive pigment agglomerates and filler texture
typical of these paintings. Work is currently under way to
study and test samples prepared by the artist and naturally aged
(20 years) as well as on model samples reproducing the artist’s
technique.