SARAH WALDEN IS accustomed to looking at things in minute detail. She often wears magnifying glasses to remove, with the use of a scalpel, caked varnish fiom the crevices of a painting. As one of the world's leading restorers, her work sometimes confines her attention, for days on end, to an area of only a few square centimetres. Yet this close-up activity, peering through what she calls 'windows' opened up on the surface of a canvas. does not prevent her fiom simultaneously asking large questions. Her previous book, The Ravished Image, carried Ernst Gombrich's imprimatur and criticised excessive restoration of paintings. lust what she meant was made d apparent at the recent Titian exhibition: enjoyment of his colour alternated with an awareness that its varying clarity and brightness owed much to different styles of conservation.

Walden is also wary of relying too much on technology. Ultimately, she insists, science can only add interesting footnotes to Walden our understanding of painting. This new book upholds her claim. Specialist knowledge of a painting's material properties is combined with extensive scholarship. It was stimulated by a commission Walden received from the Louvre to restore Whistler's portrait of his mother. An American visitor to the