New Insights into the Cleaning of Paintings

190 • smithsonian contributions to museum conservation
Table 2. Residue markers estimated by gas chromatography–mass spectrometry (GC- MS) and Fourier transform infrared spectroscopy
(FTIR). Results in italics correspond to areas where no residues were detected, and (—) indicates that no measurements were made. CS:
cleaning systems, O =: oleic acid; P = palmitic acid; PO = palmitoleic acid; S = stearic acid; V = Vulpex; W = water; WS = white spirit;
FG = fluid gel; FGP = fluid gel applied on barrier paper; RG = rigid gel; FTIR (a) 1551 cm –1 (ATR) (b) 1566 cm –1 (transmission); rd =
residues detected; nrd = no residues detected.
Cleaning System
GC- MS
O/S O/P PO/S PO/P
FTIR- ATR
(cm –1 )
Residues
P1 P2 P1 P2 P1 P2 P1 P2 P1 P2 P1 P2
VW 0.5% 0.97 — 0.71 — 0.06 — 0.04 — 1551,1566 — rd —
VW 1.0% 1.89 — 1.29 — 0.13 — 0.09 — 1551, 1566 — rd —
VW 5.0% — 3.68 — 1.75 — 0.29 — 0.12 — 1551, 1566 — rd
VWS 1.0% 0.38 1.18 0.22 0.59 — 0.12 — 0.06 — — nrd rd
VWS 5.0% 1.36 — 1.16 — 0.10 — 0.06 — 1551, 1566 — rd —
VFG 1.0% 0.43 — 0.18 — — — — — — — nrd —
VFGP 1.0% 0.36 0.35 0.29 0.20 — — — — — — nrd nrd
VRG 1.0% 0.43 0.40 0.24 0.19 — — — — — — nrd nrd
Painting 0.36 0.45 0.20 0.17 — — — — — — — —
Vulpex 16.81 10.79 1.01 0.65 1551, 1566 — —
potential for the treatment of small areas or of surfaces that
are vulnerable to mechanical action (Table 2). The amount of
potassium found on the surface (SEM- EDS) and the increase in
the pH values coincide with the results obtained by means of
GC- MS and FTIR, which highlighted the presence of Vulpex in
the painting (Table 3).
Table 3. Amount of potassium detected by scanning electron
microscopy and energy- dispersive X- ray spectroscopy (SEM-
EDS) and pH values on the treated surfaces. A dash (—) indicates
that no measurements were made. V = Vulpex; W = water; WS
= white spirit; FG = fluid gel; FGP = fluid gel applied on barrier
paper; RG = rigid gel.
Cleaning system
K ion detected
weight for P1 (%)
P1
pH
VW 0.5% 3.8 8.4 —
VW 1.0% 4.7 9.5 —
VW 5.0% — — 9.4
VWS 1.0% 0.72 6.8 6.5
VWS 5.0% 6.6 9.6 —
VFG 1.0% 0.53 6.7 —
VFGP 1.0% 0.42 6.8 6.5
VRG 1.0% 0.56 6.8 6.4
Untreated painting 0.56 6.7 6.4
P2
Assessment of Alterations on the Paintings:
Analysis of Swab Extracts
The assessment of painting surface damage from cleaning
processes based on experimental models is a complex issue: it
is difficult to extrapolate the results to real works because of
the large number of factors that affect deterioration processes.
Phenix and Sutherland (2001) focused on this problem in an article
on the effects of organic solvents on oil paint layers and
included a description of the advantages and drawbacks of some
experimental designs. Several studies carried out on paintings
manufactured in laboratories and the immersion of samples in
different solvents served to improve our understanding, in a controlled
environment, of many of the processes and risks involved
in painting deterioration (Sutherland, 2003, 2006).
Several premises that have led us to the application of cleaning
protocols similar to those used in restoration have been taken
into account for the qualitative evaluation of surface damage in
samples treated with the different cleaning systems. First, half the
treatments used in this study were not applied in liquid form, but
were gelled, and furthermore, previous publications that describe
the potential damage from Vulpex solutions with high soap concentrations
were taken into consideration. Second, the painting
in the test samples and the painting selected for the restoration
team were different, so there were fewer variables that could
have a bearing on the differences or similarities in the results if
the same cleaning and rinsing procedures were applied.
One of the markers that points toward particle dragging
with the rinsing swab is the existence of azelaic acid as well as