'Special grit' protecting National Gallery masterpieces

A special form of road grit is being used near the National Gallery in London to prevent its priceless artworks from being damaged.

Westminster Council started using sodium-free grit earlier this week after it emerged that the normal kind can cause a chemical reaction in oil paintings that leaves them with permanent discolouration.

Experts found that salt in standard grit was being brought into the gallery on the soles of visitors' feet and was placing artworks at risk of being spoilt by a blackening effect.

Paintings featuring the traditional red pigment vermilion, which is often used in Old Masters pictures, are in the most danger of being affected. It is estimated that up to 15 per cent of the pieces held in the gallery's permanent collection could be at risk of damage.

Dr Ashok Roy, director of science at the National Gallery, commented: 'We really started to notice a problem at the end of last winter but it's only after facing similar challenges with the snow this year that the issue became particularly acute.'

Old Masters currently held by the gallery include The Virgin of the Rocks by Leonardo da Vinci, Caravaggio's The Supper at Emmaus and Bacchus and Ariadne by Titian.