Screentones, or halftones, are made of a pattern of dots that provide shading. Back in the days before digital art, these tones would be bought printed on a big sheet of sticky-backed plastic. Artists would apply this large, clear sticker over their art and then carefully use a sharp knife to cut out the areas that didn't need tone on them and peel away the excess. The downsides to this method were that you had to continue buying new screentone sheets, and that, sometimes, a careless stroke would cut through your original artwork, ruining it!
But now, we can mimic these patterns of dots digitally. And, thanks to layer masks, we can simply mask out the areas that don't need to be shaded without doing any damage ...
