Historical evolution of oil painting media: A rheological study

Rheology is the science of flow, which is a phenomenon found in every painting operation, such as decorative paintings or protective coatings. In this article, the principles of rheology as applied to paintings and coatings are recalled in a first part and the rheological criteria required in the paint industry presented. Indeed, different flow behaviours leads to different finishes. The same procedure and techniques as in industry can be employed to explain some evolutions in oil painting aspects over the centuries. The first recipes for oil painting indicate the use of treated oil, resins and spirits. This article deals with the evolution of the composition of these systems as media for oil painting, according to rheological clues. During the Renaissance period, the media used were Newtonian or slightly shear thinning and allowed one a perfect levelling. Then techniques changed, paints became more opaque with less addition of oil/resin media, and brushstrokes appeared visible. Some preparations containing lead, oil and mastic resin, whose flow behaviour is closed to those required in industry, may have appeared during the 17th century and are still used and sold today.