Wall Paintings

by Peter Draper

How often in visiting a church, erased fragments of ancient, vivid depictions of often Biblical scenes displayed. The originals would have transformed the interior as well as serving as the equivalent of modern strip cartoons for the largely illiterate congregation. The lime washings over the Reformation, the Commonwealth and the well meant restorative operations of Professor E W Tristram in the interwar years all caused irreparable damage.

Tristram (1882 – 1952) became Professor of Design at the Royal College of Art in 1925 and took a great interest in these depictions. He published several works on the subject, notably ‘English Medieval Wall Painting’ in 1944 -50 and posthumously in 1955. A Kentish example and its rectification is described in the article by Fiona Allardyce in Arch. Cant. CI, 122 (1984) relating to the Painting of St. Eustace in Canterbury Cathedral. The basic error in Tristram’s method was the application of a wax coating. This sealed the surface, leading to moisture being trapped, producing Calcium sulphate from limestone and building up osmotic pressure and hence spalling off of the surface.

In a recent issue of Chemistry World (V 7, no. 10,9, (2010)) (Roy. Soc. Chemistry) is an article outlining current practices and developments. These were presented at the recent EuCheMS Conference in Nuremberg (R.Giorgi et al. Chem. Eur J., 16, 9374 (2010)). Presently an acrylic polymer coating is applied but these yellow in light and lead to the same loss of surface as the wax. At the University of Florence, a solution of Calcium hydroxide nano-particles has been developed. These do not make the surface impervious to water and react with oxygen to replace lost Calcium carbonate. The technique has also been successfully applied to paper etc. The alcoholic solution is simply brushed onto a thin layer of porous paper which is then removed when dry.