This is a new feature....a word you may have heard of but don't know what it means.
The word: PENTIMENTO
pentimento (plural pentimenti) is an alteration in a painting, evidenced by traces of previous work, showing that the artist has changed his mind as to the composition during the process of painting. The word derives from the Italian pentirsi, meaning to repent.
The Arnolfini Portrait by Jan van Eyck, National Gallery, London 1434. Among other changes, his face was higher by about the height of his eye, hers was higher, and her eyes looked more to the front. Each of his feet was underdrawn in one position, painted in another, and then overpainted in a third. These alterations are seen in infra-red reflectograms.