Accurate nondestructive studies of the metallic luster stains on ancient overglazed ceramics provide provenience data owing to the new knowledge obtained on (1) the proportion between trace elements composing this luster and its variation with centuries and continents; (2) the existence or absence all over the luster of iridescences due to optic interferences in thin films ; (3) the depth variation of these films; (4) the shape and distribution of colored mosaic microscopic areas forming the iridescence. Surface analyses with a laser microanalyzer and x-ray microfluorescence were done selectively on the luster parts, the painted and non-painted parts. Optical microscopy studies were done pursuant to the unexpected appearance of strong iridescence (similar to the Newton Rings color iridescence) which formed around laser beam impact microcraters. These laserborn iridescences were then compared to iridescence originally existing on the luster of some ancient ceramics. Our hypothesis thereupon considers as essential the combining of the metallic sheet effect (some luster elements like copper and silver are reduced to metallic state - suspended in colloidal form in the glassy surface of the luster - probably in the reducing, special lustering kiln) and the iridescence effect due to the optic interferences in very thin films (probably formed on the luster by superficial oxidation at the end of the reducing kiln process).