Forty‐eight tin‐glazed ceramic fragments (faiences) from Lorraine, found in excavations or pertaining to objects in collections, were subjected to X‐ray fluorescence analysis to determine the bulk, major, minor and trace element compositions. Sixteen superficially clay layers from the surroundings of Lunéville and Saint‐Clément were also analysed. The faiences are, with four exceptions, MgO rich. The combination of stylistic and chemical arguments allowed the recognition of 28 objects that were attributable to the important faience manufactory of Jacques II Chambrette in Lunéville. This reference group was used to test the provenance of high‐Mg faiences from private collections. The latter are not from the manufactory of Le Bois d'Épense/Les Islettes as commonly assumed, but most probably belong to Lunéville and Saint‐Clément. According to archival sources, the potters mixed three clays for the pastes. Some prospected clays are MgO rich due to the presence of dolomite and other Mg‐bearing minerals, but not as high as the faiences, a fact that can be explained by the sampling of de‐carbonatized layers.