Paper Conservation: Decisions & Compromises

The Microflora Inhabiting Leonardo da Vinci’s Self Portrait:
a Fungal Role in Foxing Spots
Guadalupe Piñar | Katja Sterflinger | Flavia Pinzari
Department of Biotechnology, Vienna Institute of Bio Technology (VIBT)
University of Natural Resources and Life Sciences, Vienna, Austria
ICRCPAL-Istituto Centrale per il Restauro e la Conservazione del Patrimonio Archivistico e Librario,
Laboratorio di Biologia, Rome, Italy
Introduction
Leonardo da Vinci’s famous self portrait is made
in red chalk on paper. It is housed at the Royal
Library in Turin, Italy. The drawing is strongly
affected by foxing spots. The damage presumably
occurred between 1890 and 1950. The portrait
has been recently brought to ICRCPAL (Rome) for
scientific analyses.
According to Corte et al. (2003) foxing is a
modification of paper occurring in the form of
brown, brown-reddish or yellowish spots, the origin
of which has not yet been clearly explained.
In fact, despite the extensive research that has
been done in this field, no conclusive results exist
to the cause of foxing. There are two different
theories concerning its development: the biotic
theory, according to which the stains are the
result of the activity of micro-organisms (Choi
2007, and references therein) and the abiotic
theory, entailing chemical phenomena such as
oxidizing and/or heavy metals deposits (Cain and
Miller 1982). In particular, the deterioration of
paper has been linked to the presence of metals
in the pulp, and paper yellowing/browning is
supposed to be caused by cellulose oxidation catalysed
by metals. There is moreover a quite clear
relationship between the occurrence of these
modifications and environmental conditions
(Gallo and Pasquariello 1989).
Recent investigations have studied the role of
fungi in foxing by light and electron microscopy
(Florian and Manning 2000). These studies found
that in some cases the initial cause of foxing was
a group of spores of conidia that had been deposited
on the surface of the paper prior to printing
and had germinated in situ during the slow drying
of the paper.
Arai et al. (1990) proposed the following process
for the formation of foxing: absolute tonophilic
fungi conidia and or ascospores attach to
paper, germinate and grow their hyphae. The
hyphae form colonies around dust particles.
These fungi metabolize mainly malic acid, cellooligosaccharides
and aminobutyric acid in the
colonies. These components react chemically
together on the materials at Aw 0.80 and 20-35°C
forming brown products and oxidative reactions
on paper that result in localised foxing spots.
From old books and manuscripts showing the
characteristic foxing discoloration more than 60
fungus cultures were identified by ordinary light
microscopy and the most common encountered
species are Eurotium, Aspergillus and Penicillium
species.
The brown-rusty spots that deface Leonardo
da Vinci’s portrait have all the characteristics
of foxing, and some of them show a blue-yellow
fluorescence that is also typical of both biological
and chemical foxing (Choi 2007).
The knowledge of the nature of the stains is
a question of great concern because future conservation
treatments and actions towards the
famous object would better be based on scientific
data. Furthermore, the delicate object has been
poorly studied from the “biological” point of
view: only a couple of swab sampling undergoing
culture-dependent techniques was performed between
1960 and 2000, and no significant results
were obtained at that time.
With the aim to address the problem and assess
the current microbiological risk of the drawing,
we performed a study on Leonardo da Vinci’s
self portrait based on non-invasive sampling
using diverse membrane filters and swabs, and a
combination of SEM-EDS imaging culturing and
molecular techniques.
Methods
Sampling
One of the main problems encountered in the
study of Leonardo da Vinci’s self portrait was
the execution of the sampling. Clearly no micro
fragments could be removed since this action
may have caused further damage to the object or
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