New Insights into the Cleaning of Paintings

number 3 • 191
palmitic and stearic acids since azelaic acid is only found in the
oil of a dry paint film. This method can only be used to perform
a qualitative estimate of the paint dragging process and does not
explain the factors behind the damage and the way in which it
may have occurred. Furthermore, the semiquantitative calculation
of the fatty acids that had been dragged with the cotton
swab may help us estimate the vulnerability of the studied surfaces
to the different cleaning treatments.
In general, the amount of azelaic acid found in the swabs
from the two paintings was low, especially in areas treated
with Vulpex in an aqueous solution or in fluid gel. The painting
treated by the restoration team showed the greatest amount of
azelaic acid extracted in the swabs, specifically in the area that
was cleaned with the solution with the highest concentration
(5%) (Figure 3).
It is important to note that in the case of the test samples
treated only with water the number of times the moist swab was
run over the surface was equivalent to the soap application and the
rinsing. No azelaic or stearic acids were found on the swab in this
case, and the amount of palmitic acid was the lowest. This means
that the negative effect on the painting surface stems from the soap
in the aqueous medium, regardless of its application method.
No azelaic acid was found on the test samples where soap
in white spirit was used in any concentrations. However, varying
amounts of dicarboxylic acid were detected in the swabs used
for the older painting (P2), especially in a dark area with umber
pigments.
The barrier paper used in test samples treated with gelled
systems did not prevent paint particle dragging, although the
extent of particle detachment was lower than in the areas where
gel was applied directly on the painting. Similarly, the barrier
paper did not prevent fatty acids from being found on the cleaning
swab from the painting treated by the restoration team. Here
the swabs showed the highest value of palmitic acid, possibly
because the painting was older and its free fatty acid content was
greater, although it is also true that the rinsed area was larger.
The cleaning treatments with rigid gels were not rinsed with
swabs; therefore, they are not included in Figure 4, where the
results of the fatty acid measurements are summarized.
Observed Damages on the Paintings
after Cleaning Treatments
Damage evaluation by means of SEM and CSM was only
performed on the P1 test samples. In these cases, controls with
water and with a rigid agar gel without Vulpex were applied to
check the effect these elements had on the painting.
SEM
Several research papers applied scanning electron microscopy
to evaluate changes in the painted surfaces after cleaning
(Burnstock and White, 1990; Hedley et al, 1990; Morrison et
al., 2007). In this study, images at 30× and 100× were used to
evaluate the changes caused by the different treatments. Images
at 500× revealed small particles and the texture of the painted
surfaces. The main types of damage observed were cracking,
FIGURE 3. Chromatograms of the extracts from the rinsing
swabs from treatments of painting P2 with (A) VW
5.0% and (B) VWS 5.0%. The top chromatogram shows
dimethyl azelate (AZ), which means that paint dragging
has occurred. The bottom chromatogram shows methyl
palmitate (P), methyl stearate (S), and a large amount of
methyl oleate (O) from the Vulpex. IS corresponds to the
internal standard, methyl nonadecanoate.