III. Painting Technique and Restoration (PDF, 5,21 MB) - Koninklijk ...

BULLETIN
BULLETIN
d. The imprimatura
A pale grey stripey imprimatura is present but not easily detected. Stripey
imprimatura is characteristic of Rubens panel paintings but it is most
commonly seen in his sketches on panel, such as the recently restored
Triumphal Chariot of Kalloo (KMSKA, inv. no 318),
where the imprimatura is ochre rather than grey.
It is often less apparent in his finished paintings, as
is the case here. It can be seen, however, in the gap
between the painted contours of the wooden post
and the sky and through the transparent brown
paint of the post (ill. 6). The imprimatura can be
seen more clearly with infrared photography (ill.
7) where it appears to have
been roughly applied with
a wide bristle brush in
horizontal and diagonal
directions (2.), changing
to a vertical direction
along the vertical edges.
Ill.6 The grey stripey imprimatura
can be seen in the gap in the paint
between the post and the sky.
Rubbed away the overlying paint
layers.
The stripey imprimatura may have acted as an
isolation layer preventing the oil of the paint layer
from sinking into the porous white ground. It
was also a device to give a tonality to the ground
without losing its luminosity.
Ill. 7 The grey stripey imprimatura
is visible under the transparent paint
layer of the tree and the wooden post.
e. The underdrawing
No underdrawing was visible or detected by infra-red photography. It is,
in any case, unusual to find underdrawing in Rubens’s finished paintings,
although more common in his sketches. An example, however, can be found
in The Farm at Laeken, (London, The Royal Collection), where “lines of
underdrawing are visible in the arm and face of the standing woman in the
centre” 8
f. The paint layer
Pigments
Analysis: a number of inorganic pigments have been identified by using
PXRF, a non-destructive method of analysis. 9 Organic pigments frequently
used by Rubens, such as red and yellow organic glazes, indigo, Cassel earth
and bitumen, cannot be identified by this method of analysis.
The following pigments were identified: white lead was identified in the
29 places that were analysed; sienna or possibly umber in the browns with
occasional traces of vermilion; vermilion probably in combination with red
earth for the reds; in the yellow highlights of the hay, lead-tin yellow with
probably a yellow earth. The greens were composed of a mixture of yellow,
probably lead tin yellow and a copper containing pigment, such as azurite,
or blue or green verditer. The blues used for clothing contained copper
indicating the use of azurite or blue verditer. However the blue for the sky
could be identified as either indigo or ultramarine / lapis lazuli. Very few
samples were taken from the paint layer. Two samples were taken from
the grey paint on the margin of the left edge. This was to identify the large
white grains that occur throughout the paint layer but predominantly in
the dark area of the roof, on the left side of the picture. Another sample was
taken in the sky to identify the blue pigment that could not be determined
by PXRF.
The ubiquitous white granular pigment was identified as lead white. The
sample taken to analyse the blue pigment in the sky can be seen in crosssection
(ill.8) where ultramarine/
lapis lazuli was identified. The
under-lying grey layer contains
chalk and lead white. Originally we
believed it to be the ground layer
but now see it as an intermediate
layer and that the ground layer is
missing. 10
Ill.8. Cross-section, taken from the sky with part of a leaf.
The blue pigment was identified as ultramarine / Lapis lazuli.
(Photograph, Antwerp University).