The principles of isotope mass spectrometry are described as a means of identifying sources of artists' materials. Four elements are considered: lead, sulfur, carbon and oxygen. For the first two of these, preliminary results show promise in dating samples of lead white and discerning between artificial ultramarine and natural ultramarine from various geographical sources. The use of the method for 'fingerprinting' sources of raw materials and pigments used by individual artsist or groups of artists, and for identifying dated production procedures used in the manufacture of certain pigments, is suggested.