Percival-Prescott warns against the routine performance of major conservation treatments (like cleaning and lining) which are largely irreversible. He believes that before a treatment is undertaken, the painting and its history should be fully discussed by curator and conservator so that the latter becomes aware of the painting's historical significance. He concedes that conservators are increasingly concerned with the preservation of the original three-dimensional structures of paintings and that lining is now sometimes avoided. He discusses recent progress made in the lining process including pressureless lining methods.