He is also believed by many art historians to be the Master of the Shadows who added to the illustration of the Très Riches Heures du Duc de Berry in the mid 15th century, long after the Limbourg brothers had produced the most famous miniatures (they and the Duke died in 1416, leaving the manuscript unfinished and unbound). By then the book may have belonged to René. The calendar scene for September, probably only partly by this master, shows the chateau at Saumur, which René owned, and where he spent much of the 1460s. He also painted the main calendar scenes for March (perhaps only in part), October and December. His spatial awareness was greater than that of the Limbourgs, and he included shadows, which are a very marked feature of the miniatures of Barthélemy. His faces, especially those of peasants, are more sharply individualised, although his figures are less elegant. Only these calendar scenes, and possibly the faces in the double-page "Procession of St Gregory" (Walther & Wolf, op cit), show his style; many other miniatures were added a generation later by Jean Colombe.