One detail in Pierre-Auguste Renoir's "Luncheon of the Boating Party" always stops me cold: the few gorgeously painted glasses at the front edge of its table. The glasses are an antidote for the staginess of the rest of "Luncheon," a small and striking detail that distracts viewers from the trickery behind the larger illusion in the painting. Beyond the staged pretense of a bunch of friends out for a good time on the Seine in 1881, remnants of red wine in their glasses leave an indelible imprint in the mind's eye...