Aquatint: Step 4, when the plate is cool you have to work out which areas require tone and how much. The rosin resists acid and enables you to apply shading to the etching. Next you need to identify the white areas and paint them with straw-hat varnish, which is acid resistant and fast drying. Don’t forget to paint the edges and to check the back of the plate. All but the painted areas (which remain white) will receive the first, lightest level of shading.