Trace impurities in very minute white lead samples removed from twenty-five paintings made between 1510 and 1909 and in eighteen samples of relatively modern white lead pigments and paint were determined by neutron activation combined with chemical separation. White lead used prior to approximately 1850 contained considerably greater concentrations of silver, copper, mercury, and manganese than is found in white lead of more recent manufacture. Improvements in the technology of lead smelting during the nine teenth century is probably responsible for the greater purity of the more recent pigments. Nineteenth and twentieth century white leads also consistently contained only a relatively narrow range of small concentrations of chromium as contrasted to a rather broad range of concentrations encountered in sixteenth and seventeenth century paints. Care was taken to estimate maximum concentrations of these elements which might have been introduced into the sampled white areas of old paintings through the addition of other pigments in visually undetectable concentrations. The appearance of an insoluble antimony compound and sizable concentrations of zinc has characterized many recent lead whites. -- AATA