Uranium content of ancient Roman glass mosaic tesserae were measured by a sensitive end-window Geiger-Müller counter in an attempt to measure accurate decay rates for Uup>2up>3up>8. As uranium + thorium content is quite low (below 500 p.p.m.), contrary to a previous report by R.T. Guenther (1912), this method is not sensitive enough and neutron activation analysis is now employed. There is no evidence that the ancient Romans used uranium oxide as a coloring agent for glass. (See also AATA 14-707).