New Insights into the Cleaning of Paintings

number 3 • 189
all tests. The restorers stopped the rinsing process as soon as they
observed damage on the paintings, so this probably had a bearing
on the widespread existence of residues.
The cleaning systems that employed a 1% concentration of
Vulpex in white spirit did not leave soap residues in the samples,
whereas those that employed a solution with 5% Vulpex did
leave residues (Figure 2). The greater concentration of this solution
has a bearing on the results, although it is also possible that
rinsing only with white spirit did not completely eliminate the
Vulpex, given the lower solubility of soap in hydrocarbons. Similar
results were presented by Ross and Phenix (2005), thus confirming
the need for rinsing with water after using white spirit,
as described for other cleaning systems (Burnstock and White,
1990). Varying results were obtained in painting P2, treated with
1% white spirit by the restoration team. This case was the only
one where differences in the existence of residues were encountered,
probably because white spirit was not very efficient as a
rinsing system.
Results were different with gelled Vulpex since no residues
were found on either painting (P1 and P2). Special attention
should be paid to the fact that the ratios between O/S and O/P in
painting P2 were lower in treated areas than in untreated areas.
The greater amount of oleic acid in untreated samples could be
caused by the fatty nature of the surface dirt, as verified by the
analyses of the cleaning swabs. However, the lack of palmitoleic
acid in the GC- MS analyses and the stress vibration of the carboxylate
group in the FTIR analyses indicate that no Vulpex soap
residues could be detected with these techniques. The incorporation
of techniques for the precise quantification of residues into
the analysis methodology will be the next stage of this pilot study.
The reduction in the contact surface between the cleaning
system and the painting, either by incorporating a thickener
or applying barrier paper, confirmed a minimized penetration,
facilitated rinsing, and reduced the amount of residues.
It is especially significant to note that rinsing with clear agar
gels resulted in a residue- free surface. This result shows great
FIGURE 2. (A) Chromatogram for Vulpex, showing the
peaks for methyl palmitoleate (PO), methyl palmitate (P),
methyl oleate (O), and methyl stearate (S). The chromatograms
of samples (B) P1 VWS 5.0% and (C) P2 VW 5.0%
are included as examples. These samples show large amounts
of methyl oleate and small amounts of methyl palmitoleate,
which serve as markers for the identification of residues. AZ
corresponds to the dimethyl azelate found in the paintings.