Aging of the paint palette of Valerio Castello (1624-1659) in different paintings of the same age (1650-1655)

It is well known, from ancient Egypt, that some pigments and colourants can change with time for light effect or chemical attack. Cennino Cennini in the fifteenth century in his book ‘‘Il libro dell’arte o trattato della pittura’’ describes the use of many pigments and their degradation. He was aware of the problems and was able to suggest the answers in the use of pigments on several supports, but he could not understand the physical–chemical reason of the alteration processes. In this study, we point out the aging effects in seven paintings, practically of the same period (1650–1655). We considered in particular green, white and blue pigments of the palette of Valerio Castello. About 150 spots were selected on works painted on four different supports, canvas, wood panel, copper and slate. For each point, several determinations were carried on the pigments and decomposition products, aiming to determine the state of conservation of the paintings, the nature of the pigments, their alteration and if the support can affect the kinetics of degradation.