The Ravished Image OR HOW TO RUIN MASTERPIECES BY RESTORATION by Sarah Walden (St. Martin’s: $13.95; 174 pp., illustrated)

I have found that there are four subjects on which it is dangerous to write anything, because all the experts disagree--so whatever you write is going to be bellicosely challenged. They are: economics, ancient coins, Oriental carpets and the restoration of paintings.

Sarah Walden’s new book on the last of these topics is nothing if not contentious. The title alone sounds the call to arms. A striking cover illustration of a restorer injecting the arm of a painted nude woman with a hypodermic syringe (to prevent blistering) gives a sinister, Frankenstein-like impression. Walden is herself a picture-restorer, who has worked on major collections in the United States and Europe. But there are far more words against restoration in this book than for it. Her main argument, insistently reiterated, is that over-restoration causes damage that can never be undone; whereas allowing a painting to sink slowly under a Brown Windsor Soup of old varnish, at least leaves something for posterity to recover. She quotes with approval a Russian expert who told her that certain American-cleaned Impressionists “now look as if they were painted with toothpaste.”

A real dilemma faces the restorer. I first encountered it 23 years ago when it was proposed to restore the heads of the Roman emperors that surround the Sheldonian Theatre in Oxford, England. It was of those stone emperors that Max Beerbohm had written, in “Zuleika Dobson”: “Here . . . they are expiating, in effigy, the abominations of their pride and cruelty and lust. Who were lechers, they are without bodies; who were tyrants, they are crowned never but with crowns of snow; who made themselves even with the gods, they are by American visitors frequently mistaken for the Twelve Apostles.”

By the early 1960s, the emperors’ heads had become little more than anonymous, sooty stumps. Yet they were the originals, carved in the 18th Century; and many people wrote to the newspapers to say they should be left alone. The opposing camp suggested that the heads should be re-carved, or there would be nothing for future American tourists to be mistaken about. And it was this side that won: The heads were re-carved and have no doubt begun a fresh decline into sooty stumps. I have a feeling that Sarah Walden would have been on the other side.

Where paintings are concerned, I have faith in her. Not because she is a trained, professional restorer--after all, most of her book is devoted to lambasting people who are precisely that. I trust her, initially, because this is a most stylishly written book; and one is entitled to have more confidence in the aesthetic judgment of somebody who writes well than of somebody who writes execrably. (For the same reason, I think art critics should take more seriously than most of them do, the little dialogue about contemporary art in Evelyn Waugh’s “Brideshead Revisited”: “ ‘It is bosh, isn’t it, Charles?’ ‘Very great bosh.’ ” Then too, Walden is pointedly unenthusiastic about modern art, and notes with ill-concealed relish that much of it is already suffering from galloping decay because of the technical sloppiness of its creators.)

It is hard to convey the vivacity of Walden’s prose without extensive quotation. Just a few samples:

“We revere antiquity, but we want to reduce it to our own terms. We trap the past, but we tease it in captivity.”

“(Rembrandt’s earlier work) when he was still a fashionable society painter, had an ingratiatingly smooth, licked finish. . . .”

“Already the unreflecting, extrovert character of the 1960s is beginning to seem as dated, and in a sense as forlorn and artificial, as mid-Victorian gloom.”

“(An over-cleaned painting) is like a symphony left with only the trumpet and drum parts, and no supporting orchestration.”

Walden attacks her prey, such as the late Helmut Ruhemann (chief restorer of the National Gallery, London) with a wit as caustic as the solvents she rebukes them for using on Old Masters. At times the book is profoundly philosophical; and she gives fascinating historical insights into the way that different periods restored pictures according to the styles current at the time--in their own image, so to speak.

It is perhaps a failing of the book that it remains too consistently on this high plane of metaphysics and Olympian historical perspective. What I expected in this polemical work, and what is missing from it, is a stroke-by-stroke account of the alleged ruination of a painting by one of the restorers she condemns--the ideal candidate would have been Titian’s “Bacchus and Ariadne” in the National Gallery, London, which, Walden considers, was ruined by Ruhemann. Perhaps she thought the technicalities would bewilder or bore the layman; but I would trust her, with her extreme prose felicity, to make the dullest details clear. If she does the same in her picture restoration, she must be a whiz.