MONDAY, 3 OCTOBER 2011War broke out on 3rd September 1939. The paintings at Trafalgar Square’s National Gallery needed to be evacuated. Some suggested that they should be shipped to Canada for safekeeping, but such an operation would have been susceptible to German U-boat attack. Kenneth Clark, the then Director of the National Gallery, received the following telegram from Winston Churchill: “hide them in caves and cellars, but not one picture shall leave this island.” And so it was that the National Gallery’s entire collection came to be stored in a disused slate mine at Manod, in North Wales, for most of the Second World War.
High on the slopes of Manod Mawr, 500 metres above sea level, a horizontal tunnel leads into the mine. Once the site had been selected as a hiding place, explosives had to be used to enlarge the entrance so that the bigger paintings would fit down the tunnel. Small brick ‘bungalows’ with concrete roofs were built within the 60 metre high caverns to house the paintings. The National Gallery’s priceless treasures were joined by all the royal pictures from the palaces, a number of paintings from the Tate Gallery and even the Crown Jewels. The entire convoy travelled to North Wales disguised as a fleet of delivery vehicles for a chocolate company.
However, even in this subterranean hideaway there were fears for the safety of the paintings. Fragments of rock regularly fell from the roof of the mine and on one such occasion a number of paintings were destroyed. It was also known that the paintings would not cope well with changes in temperature and humidity, so a crude ventilation system was devised. Air was passed over trays of dehydrated silica gel in order to absorb any moisture before being circulated throughout the ‘bungalows’ by a series of electric fans. The trays of silica gel were changed regularly and dried in an array of domestic electric ovens near the mine entrance. The entire operation was powered by an ancient, slow-speed, two-cylinder diesel engine that had been recovered from a disused brickworks.
The rudimentary ventilation system was not only successful, but also led to valuable scientific discoveries. The humidity in the mine was checked daily, something that had never previously been done, and when the paintings returned to London they were in a better condition than when they had left. Indeed, according to former Director Neil MacGregor the “scientific advances made in the underground chambers of Manod quarry changed the Gallery forever.” When the Gallery was renovated after the end of the war, it became the first gallery in the world to include an air-conditioning system for controlling the temperature and humidity within the building. The excursion to Manod also prompted the Gallery to establish a Conservation Department alongside its pre-existing Scientific Department.
Today, the Conservation Department works with curators and scientists to try and preserve works of art for the enjoyment of future generations. The Department checks the state of the paintings, controls their storage conditions and oversees major restoration and cleaning operations. A variety of physical and chemical techniques can also be used to obtain information on the different layers of a painting and the materials that were employed. Such techniques often help to elucidate the entire history of a painting, including changes made by the original artist, and later alterations or forgeries.
One method is to remove flakes of paint from damaged areas of a picture, mount them in cold-setting resin, and polish them to reveal a cross-section of the masterpiece. When these samples are examined using reflected light microscopy, the layered structure of the painting is revealed and some pigments can be identified by their colour and optical properties.
Infrared reflectography digs a little deeper. Carbon black, a form of charcoal, was used by many of the great European painters around the seventeenth century for making their initial underdrawings on a blank canvas. Carbon black is also very absorbent in the infrared portion of the electromagnetic spectrum. Therefore, by constructing an image from reflected infrared radiation, it is possible to delineate an artist’s original sketch of their composition. Sometimes, the results are not as expected. When Leonardo da Vinci’s The Virgin of the Rocks was subjected to infrared scrutiny, the conservators discovered two different underdrawings: one for the final composition we see today and the other of a kneeling woman with her face in profile and one hand across her breast. The Virgin of the Rocks that now hangs in the National Gallery is a copy of a previous painting that Leonardo had produced for a private client. It appears that Leonardo had initially planned to use a slightly different composition in this version, which was for the Confraternity of the Immaculate Conception in Milan. However, after patching up a financial disagreement he changed his mind and reproduced the original composition.
X-ray photographs reveal other aspects of a painting’s past. Heavy metals, such as lead and mercury, are more opaque to X-rays than other elements. High concentrations of these elements in certain pigments produce white areas in the resulting X-ray image. An X-ray photograph of Renoir’s The Umbrellas reveals that the woman on the left of the composition used to sport a small hat and frilly collar, whilst the painting’s background used to consist entirely of foliage with no umbrellas at all. Art critics believe that Renoir made the original painting in 1880, but, when he returned to the picture in 1885, his attitude to his art had changed. Instead of his previous agitated and feathery style, he now preferred broader brushstrokes, geometric shapes (hence the umbrellas) and a less Impressionistic style.
Modern spectroscopic methods are also increasingly being used by conservators to aid the identification of materials and pigments. Laser microspectral analysis uses a laser to vapourise a few micrograms of a sample. Elements present in the sample are then identified by emission spectroscopy, recording the wavelength of the emitted energy as atoms revert from a high energy electronic configuration to a lower one.
A recent BBC documentary investigated a painting called The Procuress, which is owned by the Courtauld Institute in London. Many art specialists attributed the work to the great Dutch master Johannes Vermeer, but spectroscopic analysis of the upper layers of paint revealed that the paint was mixed with phenol formaldehyde resin. Phenol formaldehyde, commonly known as ‘Bakelite’, was one of the first ever thermosetting plastics. In the early twentieth century it was used in everything from kitchenware to children’s toys.
However, to an art conservator, the presence of phenol formaldehyde means only one thing: the painting must be a fake. The Procuress is in fact by Han van Meegeren, a Dutch painter and arguably the most ingenious art forger of all time. He mixed his oil paints with phenol formaldehyde resin to make them harder, giving his finished works the appearance of seasoned seventeenth century masterpieces.
The use of scientific technology in the world of art conservation has come a long way since the electric fans of Manod slate quarry. Moreover, as the science has progressed, conservators have learnt much more about the curious lives led by many individual works of art.
Tim Middleton is a 4th year student in the Department of Earth Sciences