New Insights into the Cleaning of Paintings

number 3 • 207
FIGURE 4. The FTIR spectrum showing the presence of gypsum, protenaceous material, and traces of calcium carbonate,
identified by the 1400 cm –1 peak.
hydrophilic agar (Hiby, 2008; Riggiardi, 2010). It could be hypothesized
that the heat produced by the agar gel allowed the
interaction of these two materials since it enabled the cyclododecane
to reach its melting temperature (58°C–61°C), so that the
liquid penetrated into the pictorial layers and enabled the agar
to act on the surface.
ANALYSIS OF RESULTS ON
THE PREPARATION LAYERS
A small quantity (less than 1 mg) of ground material was
scraped from a fringe area of the painting. The aim of the analysis
was to identify the composition of the ground material and to
observe the morphological structure of the mixture. The sample
was analyzed with a micro–Fourier transform infrared spectroscopy
(FTIR) and with the aid of some spot tests to identify the
type of organic binder.
The ground was made with a mixture of gypsum and a
proteinaceous binder, possibly animal glue. The FTIR spectrum
shows that apart from gypsum, only traces of calcium carbonate
are found but no anhydrite or silica (Figure 4). Spot tests were
negative for polysaccharides, i.e., vegetable gums, and for starch,
e.g., flour. However, there are some traces of fats. It is evident that
the gesso mixture is lacking a binder; the white ground contains
mainly gypsum with a very small amount of animal glue. This
is probably the real reason for the great fragility shown by the
ground.
Acknowledgments
We thank Padua’s Culture Councilor for allowing the use
of the images in this paper. We also thank Paolo Cremonesi for
collaboration during the agar testing, Stefano Volpin for the scientific
analysis, and our colleague Daniela Mancin for the translation
of the text.
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