Readers may be glad to know of one aide-memoire provided by a former director of the National Gallery, Kenneth Clark, in his One Hundred Details (1938) and More Details (1941), from pictures in the gallery. From the comparison of those photographs made before cleaning with the originals after it, one can get a good idea of what has been lost since the last 'cleaning controversy' 50 years ago.
With reminders such as these, we can press for explanations of why specific changes have been made. Of course, there is no arguing subjectively with a restorer who regards aesthetics as irrelevant because unscientific. Aesthetic objects can never be safe in such hands.