Francesco Robba executed two portraits of
Charles VI of the House of Habsburg, one in marble and one in clay. Because
they are very similar, it is possible to infer two possibilities. The sculptor
first made a clay model from which he then carved a variant in stone. Another
assumption suggests a chronological sequence: the clay bust is a replica of the
stone one, thus being a later realization. The two busts can be viewed at the Baroque in Slovenia exhibition on the
first floor of the National Gallery of Slovenia.
The Baroque sculpture made of dried, i.e.
unfired, clay is a true rarity
in both Slovenia and the wider European space. The exact reason why Robba chose
to make the portrait using an unfired material remains uncertain, but it might
have been due to time and financial constraints. The fact that the bust withstood
the atmospheric conditions during its location on the façade of the Ljubljana
Town Hall is primarily due to the sculptor’s technological expertise and
ingenuity. The restoration process revealed that the outer layers are darker
and harder compared to the clay within. Besides, dark particles of dust found
in the cracks suggest that the bust, after have been modelled, was exposed to a
heat source. The belief was affirmed when samples of clay were taken and
scientific and technological analyses revealed that the statue had been exposed
to a temperature not exceeding 500 °C. This caused mineral transformation that partially
enhanced the resistance of the surface of the sensitive support. The sculptor
further improved the statue’s durability by filling the cracks, formed during
the drying process, with plaster, and by reinforcing the back side with a
mixture of natural resin and the filler, primarily composed of flysch sandstone.
Robba then protected his work with a red coating made of egg white, or
casein, mixed with pigments of red ochre and lead minium. This initial layer
was followed by a layer of copper bronze which gave the portrait a golden hue.
The X-ray imaging of the torso showed that the clay does not contain additives,
such as plant or animal fibres that would enhance its cohesion. Besides, the
statue lacks structural elements that would provide solid support, except for a
metal mounting for the head.
The fact that the bust, when lifted into an upright position, could
break was cause for concern, so the clay mass inside was examined by means of
computer tomography. It was found that except for some small hollow areas there
were no major cracks in the clay mass. Robba modelled the statue by adding
material from the inside towards the outer surfaces, ensuring strong bond
between the existing structure and the newly added material.
Although the sculptor was a great master, the portrait did not remain
intact over time. The head was broken into numerous fragments. We scanned the
torso and fourteen larger fragments of the head and made a 3D virtual
reconstruction of the portrait. We carefully examined the fragments and
discovered that the artist shaped the clay using bare hands, serrated modelling
tools, and smoothers. Particularly fascinating are the artist’s fingerprints– Robba’s personal
imprint, eternally embedded in this unique sculptural work.
So far, a number of procedures have been carried out to
reinforce the support and put together the fragments of the head. The surface
has been cleaned and the damaged paint layer strengthened. The new findings not
only enrich our understanding of the sculptor’s technique but are also crucial
for continuing the conservation-restoration procedure which aims to restore thephysical integrity of the fragmented artwork.