The border that is painted, not framed
The band of dots running all the way around the edge of the image, just inside the white wooden frame
Around the whole picture runs a border made of painted dots, which Seurat added around 1888–89, a few years after the main canvas. It is not the frame; the plain white wooden frame sits outside it. The dotted border is part of the artwork itself, painted to control the transition from the image to the wall, and the Art Institute still shows it that way.