Stippling is a kind of drawing style using only points to mimic lines, edges, and grayscale. The entire drawing consists only of dots on a white background. The density of the points gives the impression of grayscale shading. Back in 1510, stippling was first invented as an engraving technique, and then became popular in many fields because it requires just one color of ink. Here is a photo of a fine example taken from an exhibition of lithography and copperplate art (the Centenary of European Engraving Exhibition held at the Hubei Museum of Art in March 2015; in case you're curious, here is the museum's official page in English).