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Cleaning a portrait sculpture of the painter C. W. Eckersberg

In 1865 the sculptor Otto Evens (1826-1895) produced a portrait sculpture of the painter C.W. Eckersberg (1783-1853). Evens had known Eckersberg, who was both a professor (1818) and later director of the Royal Danish Academy of Art (1827-29). Evens worked for the sculptor H.W. Bissen (1798-1868), who also became both a professor and then director of the Royal Danish Academy of Art (1850-1853).

Maleren C.W. Eckersberg, in storage and before deposition to Statens Museum for Kunst. Photo Louise Cone

The portrait sculpture of Eckersberg is an original full figure plaster sculpture. That means that it is a plaster cast of an original clay sculpture. The work depicts Eckersberg sitting on a chair, in the process of drawing.

The sculpture is one of a series of four portrait sculptures, which were made by four different sculptors portraying prestigious contemporary artists. They were originally commissioned in 1863 by the so-called Exhibition Committee to be exhibited in the new building (built in 1883 - now Charlottenborg). The sculptures stood in Charlottenborgs port leading into the courtyard of the exhibition building. In 1883 they were moved to the Academy's assembly hall, and in 1905-06 the exhibition building's vestibule. Since then they have been in storage.

Statens Museum for Kunst was contacted by Charlottenborg, who wanted to donate the four original plaster casts to our collection. In light of our then up-coming Eckersberg exhibition, it was obvious to accept the works. Evens' sculpture of Eckersberg had stood for many years without protection and was therefore very dirty, as well as suffering extensive damage and loss of material. For example, the entire back of the chair was missing.

Detail, condition of the figures right foot before conservation. Photo Riccardo Buccarella

Detail, joint in the left leg, with the edge of his jacket missing.  Photo Riccardo Buccarella

The conservation of the sculpture began with a thorough cleaning - first with a soft brush and vacuum cleaner, then with an eraser and finally with magnesium oxide, MgO.

Old fills were removed, and the surface residues of the old repair materials, which were adhered to the original surface, were also removed. The legs of the figure were disjoined from the torso, then cleaned and repaired.

Detail, clean vs. not a clean surface. Photo Louise Cone

The legs have been removed and the left side is nearly done. Photo Louise Cone

This is the right leg, which was totally broken. Here you can see the rusty dowel used to hold the sculpture together.  Photo Louise Cone

Loose pieces that need to be re-adhered to the sculpture. Photo Louise Cone

The back of the sculpture, where  the back of the chair is missing . Photo Louise Cone

Detail, missing pieces of the figures jacket. Photo Riccardo Buccarella

Cleaning of the sculpture is carried out one side at a time. Here you can see a layer of MgO drying on the surface of the left side.  Photo Louise Cone

The figures left leg, with damage around the base, partially cleaned. Photo Louise Cone

Underside of the right foot. Photo Louise Cone
Foto Louise Cone
Foto Louise Cone

The foot is now glued back on to the base, and partially re-assembled.  Photo Louise Cone

The foot is in the process of being re-modelled. Photo Louise Cone

Cleaning plaster is a complicated undertaking. Gypsum is a hygroscopic (water-loving) material, which easily absorbs water. Cleaning with plain water is thus not possible, since dirt on the surface will be transported into the porous structure together with the water. When casting plaster, it releases a lot of energy - the plaster gets hot and expands, while it presses up against the mold. In this process an approximately 0.5 mm thick, crystalline, compact and resistant layer is formed on the outermost surface, this is called the casting skin.

In professional circles, some argue that cleaning will break or damage this casting skin and thus leave the plaster with a very open and exposed surface. But can we scientifically prove the existence of the casting skin and understand if and how it is affected by cleaning?

Scanning Electron Microscopy (SEM) recording of the surface as seen in cross-section.   Towards the top of the picture you can see that the gypsum crystals are becoming shorter and more compact. This top layer is presumably the casting skin. Photo CATS

The surface of the plaster as seen under the microscope before cleaning. Photo CATS

The surface of the plaster as seen under the microscope before cleaning. Photo CATS

The preliminary analytical studies conducted in CATS, Centre for Art Technological Studies and Conservation, using both Reflected Light Microscopy and Scanning Electron Microscopy (SEM), demonstrated two important points: that the casting skin presumptively exists, and that the casting skin was seemingly not affected by this particular treatment.

These results will subsequently be elucidated in a larger and more comprehensive research project that will hopefully provide more information about what is actually happening on the surface of the plaster sculptures both during the casting process and during cleaning.

The torso is cleaned. Photo Louise Cone

The figures left leg is re-attached. Photo Louise Cone

Eckersberg in the exhibition A beautiful lie - Eckersberg. Photo Louise Cone

The conservation work was concluded by re-modelling many of the missing parts with new plaster - but not the missing chair. The sculpture was then reassembled and can now be seen in the exhibition A beautiful lie - Eckersberg until January 24, 2016.

Louise Cone
Conservator for Contemporary Art and Sculpture

Updated: 26.apr.2018
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