It’s opera’s most predictable typecasting: every African-American baritone will eventually be asked to sing the role of Porgy in George Gershwin’s Porgy & Bess. The racially explicit casting was Gershwin’s firm instruction, but it does tend to point up how infrequently black baritones are asked to sing any role other than Porgy. For Gordon Hawkins, a 46-year-old baritone who has sung the role many times, the struggle is in finding a way to define Porgy as a man, rather than as a vaguely racist caricature. “He aims for nuance, some way to measure the man, not the facade… His Porgy has to have fire and flesh, he says. He’s not the beaten-down cripple that some find demeaning.”