Sulphide layers on the Cu (110) face and on polycrystalline material were studied by electron diffraction during their formation at 300°C. The slow oxidation of a Cu (110) face forms four sulphides, two of which are newly reported, in the following sequence: Sulphide I (cubic, alpha_o=33. 51Å), Sulphide II (orthorhombic alpha=chalcocite), Sulphide III (cubic, alpha_o=4.338 Å), and Sulphide IV (covellite). Polycrystalline Cu usually gave only sulphide II, III, and IV, while increasing the reaction rate prevented the formation of sulphide II. 15 references. -- AATA