Why are the plaster sculptures dirty?
Some of the plaster casts surfaces clearly show traces of dust particles and air pollution due to the porous surface of plaster.
Clay, plaster and marble – the working method of the sculptor
Many of Thorvaldsen’s works in the museum are made of plaster. They include the small studies for planned works exhibited in the basement and the original models for sculptures in marble and bronze exhibited on the ground floor and first floor.
Both the small studies and the original models were originally made by Thorvaldsen and his assistants in clay. When clay dries the shape will change and it will crack. Thorvaldsen therefore had to transform the sculptures into plaster, which is a more stable material, while the clay was still damp. These plaster sculptures are thus the original studies and models for Thorvaldsen’s sculptures in marble or bronze, the first versions so to speak, of the work, whereas the marble sculptures were often carved in several copies.
Time has left it's mark
Thorvaldsen saved all his plaster casts in his studios in Rome, and ever since Thorvaldsens’s time air pollution and smoke from the stoves in his studio and in the museum have fallen on the originally white plaster and penetrated deeply into the porous surface. On some sculptures the dirt is causing the spectator great inconvenience.
It is now possible to clean the works chemically or by laser. Often the museum will, however, only clean to a very limited extent because the surface of the sculptures may be damaged, measuring marks etc. from Thorvaldsen’s time may disappear and because the cleaning process might damage the surface of the plaster sculptures.