Most of themajor elements visiblewith XRF could be attributed to the different pigments that were identified by means of XRD. Some minor and trace elements do not appear to be directly related to the crystallographic phases but are likely to be impurities of the minerals present. The presence of niobium and zirconium traces in titanate pigment has been attributed to the titanium ore from which it was produced.[21] In Table 2 we see that niobium is present in all of the rutile-containing layers and zirconium in two of them; thus it is plausible to attribute these elements to the same or a similar source. Furthermore, the presence of molybdenum and antimony in the yellow lead-chromate containing layer 7 suggests the presence of small amounts of the yellow–orange lead molybdate and lead antimonite.[22] However, no evidence could be found for this in the XRD patterns. It is also known that the alkaline-earth elements calcium and strontium, observed in
layers 2 and 8, are encountered as minor components of barium sulfate where they substitute for barium in the barite crystal structure.