Frudakis, 65, said his prized Italian "Giudicci" clay may be older than he is and as rare as a Stradivarius. This piece of clay, he said, may have been used on his sculptures of former Mayor Frank Rizzo or the Rev. Dr. Martin Luther King Jr., and before that others may have used it on the stern Ulysses S. Grant that looks over Kelly Drive in Fairmount Park or the Lincoln Memorial in Washington.