Weight is really the key factor, and the real way ( not simple) is to do specific gravity test.
The normal method of determining specific gravity is to weigh the specimen dry (DW), then to suspend the specimen in water on a string, and to measure the weight pulling on the string (WW) (specimen weight suspended in water). Then you subtract WW from DW, and divide the difference into DW.
Lead is a heavy metal, and lead glasses weight more, by up to 30% for a similar size and