Corot painted the oil on canvas sketch titled Medieval Ruins in northern France sometime between 1828-1830. Beginning with a brief discussion of the use of painted color sketches in the development of French landscape painting, the author concentrates his comments on Corot's materials and techniques as seen in this work. The author cites Jean Leymarie's 1979 monograph on Corot. Leymarie published translations of the painter's Rome notebooks of ca. 1828 for technical information. -- AATA