Direct temperature resolved mass spectrometric studies of paintings by Sir Joshua Reynolds (1723-1792)

The unorthodox painting technique of Sir Joshua Reynolds (1723-1792) makes restoration and cleaning of his paintings a hazardous exercise. Reynolds's experiments with media are legendary and have led to fading, flaking and cracking even in his lifetime. He tried out painting methods, which he knew perfectly well would seriously threaten his paintings on the long term. He was obsessed with the excellence that he saw in the work of the Old Masters and wanted to emulate their effects, although he was probably not fully aware of their paintings methods (Northcote, 1881). While he wanted to experiment by himself, he was very strict about the use of well-established oil painting techniques that his assistants had to employ in his studio. Reynolds experimented with oil paints spiced with additives such as waxes, megilp (a partially cross-linked mastic-linseed oil gel), asphalt, diterpenoid resins such as Venice turpentine, Copaiva balsam and copal. Sometimes he didn't even use oil. All these materials not only cause defects in the paint, but make later restoration of such paintings extremely dimcult. Despite the comparatively good documentation of his methods and materials in part by his own notebooks, analytical studies are imperative to find out what materials have been used in the paintings. Furthermore it is important to know the present condition of the binding media after almost two centuries of ageing and several restoration treatments.