This historically and artistically important marble sculpture, Theseus and the Minotaur, completed in 1782 by the Italian sculptor Antonio Canova, presented cleaning problems typical of many marble pieces. This case study outlines the conservation process involved in cleaning and restoring this sculpture, undertaken by the V&A Conservation Department.
Cleaning techniques used
The sculpture was very dirty, both from the effect of pollution and the cumulative build up of grimy fingermarks. Careful testing showed that the dirt on Theseus and the Minotaur would be difficult to remove. Scrubbing the marble would damage the surface, for example by rubbing away finely carved detail, while aggressive cleaning would remove any original coating or the finely polished surface of the sculpture.
The cleaning problems were caused by the way the statue had been treated in the past. Traditional methods of cleaning and removing stains from marble include ammonia (or other alkalis), abrasives and acids. It appears that this sculpture had been cleaned with acid before it was acquired by the V&A in 1962.
Acids often have a fast cleaning effect on marble, and were popular as a result. Unfortunately, the reason they work so quickly is that they strip the surface from the marble, taking the dirt with it. The stronger the acid used, the longer it was in contact, and the more the piece was cleaned, the worse the erosion of the marble surface.
The other major problem with acids is that they can react with the marble to form salts, which usually appear as white powdery deposits on the surface once it has dried. These can look like a white powder, fine needle-like crystals or even just a slight bloom on the surface. Salts are a problem because they expand as they dry, so if they form under the surface, they can push the top layer of marble off. Again, the more acid used, the more it is applied, the worse the damage it causes. In many cases, salts may never have been a problem if the piece had not been cleaned with acid in the first place.
In the case of Theseus and the Minotaur, the conservator tested a water based treatment with a set pH. In some places, this activated salts within the sculpture. This type of salt problem is unpredictable and only becomes apparent after the surface dries. Many problems can be caused by old treatments. The risk of causing damage by activating salts is one of the reasons to avoid using water to clean marble. Even though it is thought of as a very hard and durable material, marble can be damaged if the wrong materials are used to clean it.
Cleaning can uncover problems that weren't obvious when the statue was dirty. Sometimes, parts of a statue that have been damaged or lost have been replaced. If this was done when the statue was dirty, the repair is usually the same colour as the dirty marble, becoming obvious when the statue is cleaned.
The restoration process
Like cleaning, the restoration of losses can be controversial. In the 18th century, for example, it was fashionable to have classical statues restored. Many believed that damage on these statues showed evidence of barbarism, and insisted that any damage should be made good. Restoration often involved squaring off damaged areas, adding new marble and recarving the losses. Canova himself was asked to restore figures by the classical sculptor Phidias in this way. He refused, declaring them the work of the ablest artist the world had even seen, and said 'It would be sacrilege for me, or any man, to touch them with a chisel'.
This sentiment has much in common with modern conservation ethics, where the underlying principle is to preserve as much of the original as possible. Some of Canova's original drawings and models survive, and one of these was copied to reproduce the missing part of the foot, seen here during conservation in 1972. This repair was considered acceptable because it was copied from an original source and did not remove any original material.
The last step in the conservation of Theseus and the Minotaur was to give the statue a thin coat of microcrystalline wax, which gives some protection against dirt and accidental stains. It is much easier to remove wax, and the dirt in it, than to clean a bare marble surface should the statue need cleaning in the future. Theseus and the Minotaur is now displayed in the sculpture gallery at the V&A.