You can’t be quite sure what the motives or even meaning of some of these old things, these old primary documents might be. Without the note this appears to be a happy opposite of Watermelon Eating Contest (qv.). A well appointed young black woman bathes a temporarily unhappy black baby. Surely this isn’t presentational, stereotypical or anything. It’s just an actual young black woman bathing an actual baby. Then you might get an inkling. Look it up (Musser, for instance). The joke is that she’s trying to wash the black off. Alas.