atw International Journal for Nuclear Power | 04.2020

atw Vol. 65 (2020) | Issue 4 ı April
RESEARCH AND INNOVATION 228
| Fig. 5.
A landscape painting with a large oak tree, assigned to a 19 th century artist.
available with additional options like
automated scanning of the surface of
the painting and automated recording
of the data from the investigated
object. Further optimizations are
precise, very small irradiation spots in
so- called Micro-XRF instruments
using collimating X-ray lenses. The
advantage is at hand: The area under
investigation is much better characterised
and the imaging resolution is
higher, while the scanning over the
whole surface reveals a complete
image of the elemental distribution.
These X-ray images seem much better
achievable than to expend high efforts
for neutron activation radiographies,
although it should be reminded that
low-Z elements are difficult or not at
all detectable in XRF because of the
attenuation of their characteristic
X-rays in the paint layers. Modern
scanning Micro-XRF instruments are
operated in investigations of important
art objects like in the actual
analysis prior to the restoration of
Rembrandt´s painting “Night Watch”
of the Rijksmuseum in Amsterdam
[12].
In the following example measured
at TÜV NORD – the case of a landscape
painting from the 19 th Century
– the power of X-ray radiography
combined with XRF analysis is
demonstrated (Figures 5 and 6). The
painting, showing several traces of old
damages, had been restored earlier
and by this occasion had been relined
(this means, a second canvas was
glued on the backside). The XRF
results from the elements in the paint
layers were consistent for the pigments
expected like iron (pigment
Siena or Umber) and manganese
( pigment Umber). The detection of
chromium (pigment Chrome Green
from the beginning of the 19 th century,
or the improved version of
hydrated chromium oxide, which
became known as Viridian Green
during the 1860’s) allows to date the
painting into the 19 th century. Before
the introduction of these chromium
pigments, green colors in paintings
were mostly based on copper pigments
like Azurite, Malachite or
Verdigris, however, the element
copper was not detected in the XRF
spectra of this painting. It is worth
noting, that similar XRF pigment
analysis is well suited to detect fake
paintings if the forger used modern
pigments like Titanium White (available
since ca. 1920) or various
Cadmium pigments (not available
before the very late 19 th Century), as it
was discovered in a number of cases of
art forgery. The most prominent case
might be the forger Wolfgang Beltracci
who specialized on fakes of Expressionism
painters from around 1900
and probably sold hundreds of fakes
into the art market. In one of his
forged paintings of the famous painter
Campendonk, the pigment Titanium
White was measured in a technical
investigation with XRF, which proved
that the painting was a fake and
thereby uncovered one of the largest
cases of art forgery.
In the landscape painting of
Figure 5, surprisingly a high amount
of mercury (an element, which is
umambiguously assigned to the red
pigment Cinnabar) was detected. The
idea, that Cinnabar could have been
used in one of the paint layers below
the visible surface was at hand. By
means of the digital X-ray radiography
of the painting, it was discovered that
the artist had used an older canvas
with a mythological or religious
figural scenery for his work (see
Figure 6) and that the overpainted
and hidden composition is well
consistent with the use of Cinnabar
pigment, which often occurs in (red)
clothes of the figures.
As it was stated above, X-ray
radiography is not limited to paintings
and this is shown in the following case
[13]. Near the village of Schortens
in Friesland, a part of North-West-
Germany, a large cemetery field from
the early middle-ages had been
discovered in the 1970’s. The archaeological
findings, attributed to a period
from the 5 th to the 12 th Century,
consisted of cinerary urns including a
variety of corroded metallic artefacts
and are conserved in museums today
(Landesmuseum Natur und Mensch
Oldenburg and Landesmuseum
Hannover). However, most of the
metallic artefacts were never investigated,
although the presumed keys,
buckles, knives or even swords given
to the graves of the dead would reveal
additional knowledge about the life in
these early populations of North-
West- Germany, before and during the
Christianisation phase. The effort to
restore such objects is very high and
restoration is under the risk of
damaging the objects during the
delicate procedures involved. Hence,
a non-destructive imaging by X-rays
was chosen in order to reveal first
insight into the corroded pieces and
prepare a decision basis for later
restoring.
As an example for the results,
Figure 7 shows the amazing pictures
of a so-called needle tubule, which
was an important part of women´s
equipment in the early middle ages,
| Fig. 6.
X-ray radiography (30 kV, 4 mAs, © TÜV NORD EnSys) of the painting from Fig.5, showing the older and
overpainted composition as well as structural information.
Research and Innovation
Radiation in Art and Cultural Heritage ı Frank Meissner and Andrea Denker