On the change of refractive index of linseed oil in the process of drying and its effect on the deterioration of oil paintings

Abstract

The following paper is the results of experiments undertaken for the information of the Committee appointed by the Royal Academy to investigate the problems affecting the durability of pictures. One of the main defects of the modern picture in oil is that in course of years there is a lowering of tone over the whole of the picture-in contrast not only to the early fifteenth-century pictures in oil, but to many of the later schools of painting, such as the Dutch pictures. As the medium-linseed, walnut or poppy oil-is the same, and as the modern painter uses in many cases the same pigments, and in other cases superior substitutes, the cause of this lowering of tone must be found rather in the unscientific methods of using the materials than in the materials themselves. This view is confirmed by the fact that an examination of modern pictures-by which I mean pictures painted in the last hundred years-reveals marked differences in the extent to which lowering of tone has taken place. The pigments, if properly selected, being permanent under the conditions in a picture gallery, the lowering of tone must be ascribed to the medium. This necessitates a study of the properties of the medium with a view to finding out the reasons why lowering of tone takes place.