From Mark Richmond, Trustee, National Gallery, London
Your recent article on picture cleaning at the National Gallery (Forum, 3 June) seriously misleads your readers. Michael Daley argues that organic solvents commonly used to remove natural resin varnishes from Old Master paintings causes damage by extracting (leaching) “plastic components” of the paint films. He cites as evidence the weight loss experienced by test samples of oil paint when immersed in polar solvents. These experiments do not serve as a model for picture cleaning, and it is no surprise that 12-year-old and 400-year-old oil paint behaves differently in response to solvents.
Reliable evidence comes from the large number of analyses we have undertaken of real paint samples from paintings – of all periods and of all schools – in the Nationals Gallery’s collection. Particularly significant are the analytical results acquired using gas chromatography linked to mass spectrometry of areas of paintings where varnish has been removed mechanically, when compared with those where the varnish has been removed using solvents.
The results show that leaching of paint layers in easel paintings of any significant age during cleaning is the chimera most conservators have always known it to be. Instead, they quite properly concern themselves with the issues and practicalities of preserving paintings for the enjoyment of the public now and for future generations.
