A study of unusual degradation on a seascape painting associated with the use of zinc white pigment

Summary The authors investigated the reasons for the poor condition of S.S. Buda, painted in 1889 by G. Thomson, a gouache/watercolour on medium-weight cotton/linen rag paper. The paper was generally severely discoloured and it was concluded that this was due to a combination of photodegradation and sulphur dioxide pollution. The work of art included some passages painted in zinc white and there were some particularly unusual effects associated with this pigment. These included an efflorescence, which was shown to be zinc sulphate, causing blistering effects and the raising of the paper into a ridge. A further effect was a paler colour in the paper beneath and around the zinc oxide giving a paler ‘halo’ on the front of the image. This was in contrast to the darkening effect on paper which zinc oxide usually promotes. This latter effect was thought to be due to zinc oxide acting as a base and protecting the paper from the acids associated with sulphur dioxide pollution.