New Insights into the Cleaning of Paintings

186 • smithsonian contributions to museum conservation
In some cases, the pH value in the diluted solutions of these materials
is high, so the risk to paintings treated with these systems,
especially unvarnished ones, is consequently also high.
Several studies have been performed to optimize cleaning
systems by adding various thickeners to reduce the hazardous
effects of solvents and aqueous solutions on vulnerable surfaces
(Wolbers, 2000:74–84; Cremonesi, 2004; Campani et al., 2007;
Anzani et al., 2008; Sánchez- Ledesma et al., In press). Furthermore,
other studies have been carried out to quantify the residues
and their potential effects on the paint layers (Bueno et al., 2004;
Stulik et al., 2004).
Some tests have shown that the use of barrier paper between
the gelled system and the painted surface may provide another
alternative to protect the paint against damage from cleaning
interventions (Sánchez- Ledesma et al., 2008b). But this requires
great skill to ensure the joints between the different applications
are unnoticeable; therefore, it is more efficient for local use.
Since the 1970s, Vulpex soap has been recommended for the
field of restoration. Vulpex is manufactured only by Picreator
Enterprises Ltd. (London), who have the registered trademark
(Conservation by Design, 2005; Ross and Phenix, 2005). It is an
alkaline soap, described as potassium methylcyclohexyl oleate.
It was not until some years later that the risk that this material
posed for painting cleaning was mentioned (Carlyle et al.,
1990; Southall, 1990; Osete- Cortina and Doménech- Carbó,
2005). The erosion that an aqueous solution of Vulpex with a
pH value of 11.2 caused on a varnished painting was reported by
Burnstock and White (1990). Similar effects were later observed
on artificially aged paintings, so the authors recommended the
use of diluted solutions followed by a double rinsing of the surface
to diminish the risk from this product (Ross and Phenix,
2005). Recent preliminary studies have shown the presence of
Vulpex residues and damage on the surface of test samples from
young unvarnished paintings with 1% aqueous and 2.5% white
spirit solutions (Sánchez- Ledesma et al., 2008a, 2009).
The long history and permanence of Vulpex in the specialist
market suggested the need to complement the available information
with studies that included other theoretically safer methods
for the application of soap on a vulnerable support such as unvarnished
paintings. These methods involve mixing the soap with
a hydroxypropyl cellulose fluid gel (Klucel G) that is applied on
Japanese paper acting as a barrier and on an agar rigid gel. The
work with this model can be used as a reference to study other
commercial soaps in the specialist market. The effect of applying
and rinsing the different systems has also been evaluated with a
group of professional restorers. The results of this study, including
references from previous research, were sent to distributors
for their incorporation into the technical files. This study is completely
free of commercialism by the authors and the distributors
of materials who have supported it.
MATERIALS AND METHODS
Experimental Paint Surfaces: Test Samples
Tests were carried out on two different paintings: P1 and P2.
P1, an oil painting with 10 years of natural aging and no historic
or artistic value, was used for all experimental tests. The size of
each test sample was 1 × 2 cm for the analysis by polarized light
microscopy, scanning electron microscopy (SEM), gas chromatography–mass
spectrometry (GC- MS), and Fourier transform
infrared spectroscopy (FTIR) and 2 × 2 cm for the confocal scanning
microscopy (CSM) analyses.
P2 is a 1958 oil painting from a private collection (obtained
specifically for this study) used by the professional restoration
team for treatment tests. This painting had a seemingly uniform
layer of dirt on its entire surface. It was divided into 24 sections
by means of a water mark, and the various cleaning treatments
were applied on the different sections (Table 1).
Table 1. Cleaning systems. V = Vulpex; W = water; WS = white spirit; FG = fluid gel; FGP = fluid gel applied on barrier paper; RG =
rigid gel.
Cleaning
system Description Paintings
VW 0.5% Aqueous solution of Vulpex at pH 10.5 P1
VW 1.0% Aqueous solution of Vulpex at pH 11.2 P1
VW 5.0% Aqueous solution of Vulpex at pH 12.2 P2
VWS 1.0% Vulpex in white spirit in concentrations of 1.0 % (v/v) P1, P2
VWS 5.0% Vulpex in white spirit in concentrations of 5.0% (v/v) P1
VFG 1.0% Aqueous solution of Vulpex at pH 11.2 gelled with hydroxypropyl cellulose (Klucel G)
with a 3% concentration that resulted in a fluid gel; this gel was applied directly on the painting surface
P1
VFGP 1.0% Aqueous solution of Vulpex at pH 11.2 gelled with hydroxypropyl cellulose (Klucel G)
with a 3% concentration that resulted in a fluid gel; this gel was applied on a barrier Japanese paper
P1, P2
VRG 1.0% Aqueous solution of Vulpex at pH 11.2 gelled with agar with a 3.5% (w/v) that resulted in a rigid gel P1, P2