'To keep the colours fresh, alive and bright': the influence of preparatory layers on the durability of oil painting, according to North West European recipe books 1550–1900

Preparatory layers (size and ground) exert an important influence on the durability of a painting. This has been proved through technical studies of paintings, but is also evident from the continued attention in historical recipes to the effects of preparatory layers on paint stability. This paper explores the types of degradation described in preparatory layer recipes, their causes, and solutions offered by historical authors to prevent degradation from occurring. A survey of some 650 recipes for preparatory layers from North West European sources 1550–1900 demonstrates that choices made during the creation of a painting were not only guided by immediate results, but also that artists anticipated the long-term effects of these choices. Not only did historical authors discuss the impact of choice of ground materials, layer build-up, structure and ground colour on a painting’s stability, but artists were also warned that even the quality or thickness of layers as unobtrusive as a size or isolation layer could influence a painting’s longevity. Some authors also included advice to prevent degradation from occurring. Historical authors focused mainly on two types of degradation: delamination and discoloration. Ground thickness and the age of the ground before paint application were considered influential. The fact that advice to improve the stability of the ground is found into the last decades of the 19th century reveals the continued search for better support preparation; a flawless preparatory system had not been found, notwithstanding innovations introduced during the period and claims on the success of improvements that often accompanied ‘new’ ground formulations.