Art restoration is supposed to be a delicate, respectful craft, but recent disasters suggest a shocking truth: some restorers might be experts in chemistry and cleaning—but hopeless at painting. And when you touch centuries-old masterpieces without understanding the language of paint, the results can be, well… tragic. Take Piero della Francesca’s The Nativity  at the National Gallery. After three years under the conservators’ care, what emerged was a botched painting that loo