The rate of deterioration of Italian Renaissance fresco paintings has greatly increased in many cases during the 20th century, due to air pol lutants, especially SO₂. Of 6 northern Italian fresco paintings recently examined, all except one, which had a calcium carbonate efflorescence, showed evidence of extreme sulfatization; the efflorescence present was gypsum, calcium sulfate. Development of a treatment involving impregnation with water soluble barium ethyl sulfate, barium hydroxide and glycerine (as humectant), to produce a stable deposition of barium sulfate, is described. Identification of pigments on two of the frescoes was carried out. Ultramarine, azurite, red ochre, yellow ochre, green earth, a black pigment which appeared to be raw umber, and possibly white lead, Identifications were made primarily by emission spectroscopy and x-ray diffraction.