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Opposite: Leonardo da Vinci, St John the Baptist, 1513Ð16Left: Vincent van Gogh, Sunfl owers, 1888 (oil on canvas)cleverly painted over to make the painting look old. Microscopic examination of the painting showed pencil lines in areas of fi ne detail, a technique uncharacteristic of Renaissance paintings. This forgery is probably of 19th century origin.Science can also aid archaeology and art historians. Two vivid examples are the Shroud of Turin and the identifi cation of Richard III’s remains. In the former case, despite strong belief that the linen cloth revered by theologians was the shroud that wrapped the body of Jesus Christ after the crucifi xion, extensive research using carbon dating and microscopy has confi rmed beyond all reasonable doubt that it dates from AD1260–1390 and has to be labelled as an object of fantasy. In contrast, carbon dating and DNA analyses confi rm indisputably that the bones found under a Leicester car park belong to the Plantagenet King Richard III who was killed at the Battle of Bosworth Field in 1485.Over-painting is common in the art world, in order to re-use canvases or cover mistakes. Exposed to X-radiation, paints fl uoresce and individual elements can be identifi ed, enabling previous images to be re-created – even if the visible layer contains lead. These advances allowed Australian art historians to discover a self-portrait of Impressionist artist Arthur Streeton (1867–1943) beneath a canvas blanked with a coating of white lead paint. Using this kind of technology may well reveal a host of hidden artworks beneath even our most famous paintings. For instance, curious scientists discovered a ‘secret’ ecclesiastical image when they x-rayed Torre dell’Orologio in Piazza San Marco by Francesco Guardi (1712–1793) from the Academy of Fine Arts in Vienna. Beneath the visible oil paint they found the image of a woman with a veil (probably St Mary) holding a cloth near where a small baby lies. The head of an ox, two long ears of a donkey and the face of a man with a bald head, presumed to be St Joseph, are discernible. The under-painting was possibly the work of Guardi, or his father or brothers (also painters).Pigments and dyes derived from minerals, plants and insects each have a specifi c chemical profi le. Painters like van Gogh, Monet, Rembrandt and Rubens are known to have shown preferences in the pigments and dyes that they used; this information is potentially useful in detecting fraud. Science has also shown how colours can change over time. Many works, including van Gogh’s Sunfl owers, Peter Paul Rubens’ The Fall of Phaeton and Salvador Dali’s Portrait of Laurence Olivier in the Role of Richard III differ now from the way they were painted: dyes and pigments can change following long term light exposure (including UV), environmental contamination, contact with human hands and humidity. Detective work has revealed that van Gogh’s style of painting and choice of pigments changed dramatically after his mental collapse in 1888. He chose lead chromate (chrome yellow) in his Sunfl owers series, however the paintings today appear less vibrant than they did originally because the chrome yellow has degraded and darkened over the years.Since Renaissance times, many varnishes have been used in the protection of paintings, including egg white, tree resins (mastic and dammar), fossil resins (copal), and insect excretions (shellac). Some varnishes intensify the brilliance of original pigments, while others can cause changes (varnish is making the yellows in van Gogh’s Flowers in a Blue Vase turn a greyish-orange). Work in the National Gallery of Art in Washington shows that varnishes of older paintings fl uoresce a lot less than those of newer artwork. This is useful in identifying where paintings have been re-touched, as in examination of The Gerbier Family by Rubens. Finally, curators taking advantage of best scientifi c knowledge, are able to improve irreplaceable artwork to a standard that we can appreciate. Curators at the Institute of Conservation in London have studied works by Leonardo da Vinci and shown that the oil-on-walnut St John the Baptist in the Louvre (Paris) is in a bad state. Leonardo had special preferences for media and pigments, but many – as in his Last Supper in Milan – have deteriorated. Restoration is inadvisable as it would “not take much to destroy St John”, but by using the latest technology it will be possible to stabilise the masterpiece. Science shows that restoration need not be detrimental in conservation. ■Images: St John the Baptist, Louvre, Paris, France/Bridgeman Images; Sunfl owers, National Gallery, London, UK/Bridgeman Images.ART AND SCIENCE www.nadfas.org.uk NADFAS REVIEW / AUTUMN 2016 39