Think of Rembrandt and you think of the late self-portraits, those ruthless examinations of a lived-in face speaking of pain, regret, resignation and fortitude in the face of senescence. But take the portraits one by one and the expressions differ, even among those painted in 1669, the last year of his life. There is more pain in Self-Portrait at the Age of 63; more fortitude in Self-Portrait with Two Circles; more resignation in Self-Portrait Wearing a Turban, believed to be the last he painted. The poses are similar, but the minor changes in the furrowing of the forehead, the knit of the brows and the set of the mouth create impressions as subtly different as the performances of a great stage actor on successive nights. Are we looking at the “real” Rembrandt, or is it a perf