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Science
Neutron beams are much more suitable than X-rays for scanning bronze statues.
Good news for our art collections?
Jos Wassink
Hercules’
head
historian and Rijksmuseum curator Prof. Frits Scholten, began his doctoral research with Prof. Joris van Dik’s research group at the Faculty of Mechanical, Maritime and Materials Engineering.
Van Langh’s point of departure for any research is often a hunch that something about a sculpture is not quite right. This was also the case with the 35 centimetre sculpture of the Greek demigod Hercules, attributed to the sixteenth century sculptor Willem
van Tetrode. X-rays had been made of the sculpture before, but they had not shown sufficient contrast due to the thickness of the material.
So Hercules went to the Neutra facility at the Paul Scherrer Institute in Switzerland. The neutron beam used here comes from a spallation setup: a lead plate that is bombarded with protons delivering 600 MeV of power. The resulting neutron beam is first slowed down and then conducted to ‘the object’. As there is very little interaction between the neutrons and the material, the penetrating capacity is higher than that of X-rays. In addition, neutrons are sensitive to hydrogenous materials, such as resin and wax, thus also revealing information about soft materials. To make it even better, the neutron images from Switzerland are tomographic: the sculpture was rotated 1 degree before each following image. Three hours and 180 degrees
later, the 3D dataset was complete. “Wow, look at that!” Van Langh calls out as, on his monitor, he navigates through the inside of the sculpture up towards the Hercules’ head. Nothing remains hidden here. It is decidedly strange that no iron core pins are visible on the inside of the Hercules sculpture, but that core material can be seen in the arms and legs. The absence of core pins means that the sculpture is not a direct cast but a copy.
Something else is strange about this sculpture: the torso is hollow but the arms and legs have core material. As if someone had scraped out the top of the sculpture. But how is that possible if the sculpture is closed? The X-rays had revealed cracks in the hair. Did this suggest that the crown had been cast on separately?
Close examination of the neutron images revealed a thick lump of bronze behind the nose. Van Langh thinks the inner mould was
damaged during the casting process. Pieces of the inner mould material consequently
fell into the gap, blocking the flow of bronze to the head area, which
resulted in a sculpture without a crown. The makers then filled the head (as the neutron images clearly show) and made a new mould for the missing part. A good piece of
craftsmanship, as nothing can be seen on the outside.
‘Neutron tomography is a powerful technique because it provides
genuine ‘insight’ into these objects,’ Van Langh writes. He believes that when studying works of art one should also note how they were made - something which is not done often enough. Van Langh would love to put the entire oeuvre of a well-known sculptor through the neutron scanner. That could reveal more about a person’s typical way of working and how it develops. It could also result in the sculpture being attributed to someone other than would otherwise be the case on the basis of style features alone. ‘We should look at these works differently,’ the PhD candidate says in summary. Although he also knows that in saying that, he will kindle the wrath of the more conservative curators.
Robert van Langh: ‘Technical Studies of Renaissance Bronzes’, PhD supervisors: Prof. Joris Dik (TU) and Prof. Frits Scholten (UvA).
strange man
“The sculpture was initially considered a full-length portrait of William of Orange and attributed to sculptor Hendrick de Keyser (who also sculpted his memorial stone in Delft). The walking pose and strange posture later suggested a walking musician (a player of the violone, an early form of viola da gamba and cello). The X-radiograph revealed a strange ‘hatch’ (a flap with a rounded top) in the back of the sculpture, for which there was no apparent explanation.
With the aid of neutron radiography and tomography it could be established that the arms and lower legs had been cast on separately (and not cast in one run). This led us to believe that the sculpture was originally intended to be a moveable man, like a clockwork doll or an automaton (wind-up toy). This also explains the walking position. In this case the ‘hatch’ on the back would have been an opening for the winding handle to start the walking mechanism. These sculptures were especially made in Southern Germany in the sixteenth and seventeenth centuries.
The conclusion, therefore, was that the sculpture had originally been intended as an automaton but that it was later decided to fixate it as a standing figure and to seal the hatch in its back. Consequently, the sculpture is no longer attributed to De Keyser but is now listed as an automaton figure of a walking nobleman, made in Southern Germany (Neurenberg or Augsburg), c. 1580-1600. This case illustrates beautifully how collaboration between art historians and scientists can lead to new insights.” (Frits Scholten)
Renaissance bronzes (from the fifteenth and sixteenth centuries) are an important collection within the Rijksmuseum. Until recently, art historians only ever studied the style features. Exactly how the sculptures were made was of little importance to them however, partly because this was barely visible.
Now, new techniques based on neutron tomography reveal every detail of the hidden inside. Not only does this enable one to learn more about the artist, it also facilitates the distinction between an original and a copy. That could be a matter of millions. Robert van Langh (44) is no average PhD candidate. He considers himself a late developer. Upon leaving secondary school he went to a retail school in Breda, after which he trained as a goldsmith in Antwerp. He learned to restore fine art at the Antwerp Institute for Fine Arts. His interest in the scientific aspects of the various works of art led him to research institutes in New York and Florence. In 2006 head of conservation & restoration Van Langh, encouraged by art
‘Neutrons are sensitive
to
hydrogenous materials
such as resin and wax’
Robert van Langh: “Neutron tomography is a powerful technique.” Photo: Sam Rentmeester Photo: Ri jksmuseum (16083) Photo: Ri jksmuseum (1954-43)
