The philosophy of modern conservation is different from that of previous eras: the emphasis now is on long-term stabilization by methods that alter the structure of a painting as little as possible. Nevertheless, if paintings are obscured by discolored varnishes and old repaints, they are cleaned, and this has often led to anxiety and debate as long-admired images are transformed.

This Guide discusses the material nature of paintings and the ways that they have changed, both naturally and at the hands of previous restorers, and it describes the main types of conservation treatment carried out on panel and canvas paintings and some of the complex issues involved in cleaning and restoration.