Title
Proposal Nº
EXPERIMENTAL REPORT
Autoradiographs from the painting “St. Sebastian“ (c. 1649)
by Georges de La Tour
162 x 129 cm2
Name(s)
Principal Proposer:
Affiliation
Instrument
B8
Local Contact
Dr. B. Schröder-Smeibidl
Date(s) of Experiment
C. Laurenze-Landsberg, Gemäldegalerie Berlin (GMB)
Experimental Team: C. Laurenze-Landsberg, C. Schmidt (GMB)
Dr. C.O. Fischer, Dr. B. Schröder-Smeibidl (HMI)
Date of Report
Neutron activation autoradiography (NAAR) is
used in the examination and analysis of the materials
and techniques of paintings. X-ray-radiography
principally indicates the distribution of the heavy
elements like in the pigment lead-white. In contrast
NAAR is capable of revealing different coloured paint
layers piled-up during the actual creation of the
painting. In many cases the individual brushstrokes
applied by the artist are made distinctly visible as well
as changes or corrections that were made during the
painting process. By using paintings that have been
reliably authenticated it is thus possible to identify the
particular style or “handwriting” of a specific artist.
The first step is to expose the painting to a flux of
cold neutrons (Φn=1⋅109 cm-2s-1) at the instrument B8
at the BER II. After irradiation the neutron-induced
radioactivity decays with time. Around a dozen
different isotopes are created which emit beta
(electrons) and gamma radiation. The most important
isotopes and their half-lives are: 32P, 14.2 d; 56Mn, 2.6
h; 60Co, 5.3 d; 64Cu, 12.8 d; 76As, 1.1d; 122Sb, 2.8d;
203
Hg, 46.6 d. In the second step the area distribution
of the induced radioactivity of the isotopes in the
pigments is recorded as images depending on the halflife times of the isotopes. In the present investigation
imaging plates (Fuji BAS 2000, 20x40 cm2) were
applied which are ten times more sensitive compared
to X-ray films. The recorded information is read by a
laser scanner and digitally stored. In addition a Gedetector is used to analyse the entire radiation from
specific locations on the painting.
Georges de La Tour (1593–1652) was a French
court painter and a contemporary of Rembrandt. After
his death the painter disappeared into 250 years of
obscurity. Then in 1915 H. Voß, an art historian from
Leipzig, discovered three by the artist signed paintings.
Since then about 45 paintings have been accepted as
original works by La Tour, although the majority is
unsigned. They were recently exhibited in three major
exhibitions in Washington (1996), Fort Worth (1997)
and Paris (1997/98).
Among the paintings that have been ascribed to
the artist are several that repeat specific themes or are
even exact replicas of each other. There are 12
versions world-wide of the referred composition, with
8.3.2001
the theme, “The depiction of St. Sebastian” tended by
Irene: 10 with horizontal and 2 with a vertical shape
like the painting in Fig.1. These latter paintings belong
to the Louvre in Paris and the Gemäldegalerie
Figure 1: Georges de La Tour,
The Depiction of the St. Sebastian (c. 1649),
Gemäldegalerie zu Berlin
in Berlin. The Louvres version is accepted as being an
original whereas opinions were divided as to whether
the Berlin painting is a replica produced by the master
himself or a copy by his son Etienne. Since the
Gemäldegalerie also owns fully authenticated works of
La Tour, an investigation of paintings using NAAR
was carried out to clarify the issue of authorship by
comparing painting techniques.
To complete the examination a X-ray radiography
was performed (Fig. 2). Lead cannot be activated by
cold neutrons, therefore its presence is invisible in
neutron autoradiography but it is seen in the X-ray
transmission picture. Lead white is the most dense
pigment employed in a painting and was the only white
colour available to the “old masters”. It is particularly
effective at absorbing X-rays and therefore where it is
present the X-ray film remains
Figure 3: 2nd neutron autoradiograph, composed of
32 imaging plates, exposure 1d 3 h to 1d 6 h after
activation.
Figure 2: X-ray radiograph of St. Sebastian, by
permission of Staatliche Museen Preußischer
Kulturbesitz, Gemäldegalerie Berlin
unexposed. The paintings stretcher is also readily
visible since the thickness of the wood is far bigger
than that of the layer of the paint.
The two most informative autoradiographs are
illustrated in Fig. 3 and Fig. 4 showing the sets of 32
digitally processed and assembled plates. In Fig. 3, the
2nd autoradiograph reveal paint layers containing the
blue pigment azurite (64Cu), only applied to the the
lighter parts of the mourner’s veil. The strongly linear
brushstrokes have been observed in other paintings by
La Tour and also the use of reserve space for the
praying hands and the shadow of the arrow in
Sebastian’s chest. In the 3rd autoradiography (Fig.4)
the distribution of mercury (203Hg) included in the
pigment vermilion is recorded. This red pigment was
used in Irene’s dress and in the lighter parts of the flesh
tones. The contour of the figures have been reinforced
with bone black containing 32P. This can be seen as a
continuous line that lies approximately 0.5 cm outside
the finished painted form. The fact that adjacent paint
layers do not overlap and that there is a small gap
between the painted forms suggests together with the
presence of incisions, that cartoons were used in the
construction of the painting. This is also a technique
that has been identified in several other works by the
artist.
To summarise and conclude the autoradiographs
of the Berlin “St. Sebastian” have revealed painting
techniques that are fully in accordance with those
Figure 4: 3rd neutron autoradiograph, composed of
32 imaging plates, exposure 5d 4 h to 7d 2 h after
activation.
techniques that are fully in accordance with those
found in secure works by La Tour.
C.-O. Fischer et. al., Nuclear instruments & Methods
in Physics Research, A 424 (1999) 258