New Insights into the Cleaning of Paintings

32 • smithsonian contributions to museum conservation
The SU data sheet makes the conservator observe more rigorously
the different strata and their relationships during the cleaning
process and compels the restorer toward a logical approach
to complicated stratigraphic situations. With this system of documentation
the conservator must necessarily approach the cleaning
process from an analytical point of view, attentive to details and
cautious in the identification of each SU. This system of documentation
requires layer by layer removal, identifying and studying
each new SU and its relationships with the other units. This allows
a standardized documentation to be obtained that can be
studied by any given researcher in order to understand how the
nonoriginal layers were arranged before cleaning and exactly how
the cleaning was carried out. Basically, the main idea is to think
of the cleaning process in terms of an archaeological excavation.
This methodology has been used for the documentation of various
cleanings, with very good results (Barros García, 2004, 2009).
PRACTICAL APPLICATION
The system can be illustrated with the example of the recording
carried out for the cleaning of the panel painting St.
Matthias and St. Philip by Paolo da San Leocadio (second half
of the fifteenth century), which is in a private collection in Madrid
(Figure 1). In contrast to the original layers, the materials
deposited over time can be removed following a stratigraphic
approach during cleaning (Figure 2). This approach provides a
great amount of information, which is not always easily accessed
by mere observation of the surface or cross- sectional studies. The
main nonoriginal layers identified in St. Matthias and St. Philip
were the following: dirt (SU1), overpaint (SU4, SU5, SU6, SU7,
SU8, SU9, SU10, SU12, SU15, SU16, SU17, SU18, SU19, SU20,
SU21, SU22, SU24, SU29, SU33), varnish (SU2), fillers (SU13,
SU25, SU27, SU28, SU30), and wax (SU31).
FIGURE 1. The painting during the cleaning process (detail).