Instead of lines, one can also etch shades (different values of grey). First, varnish powder, resin or asphalt powder is evenly scattered onto the plate. Then the plate is heated to melt the resin. The acid will then corrode the plate around the varnish particles, thus etching a shade that consists of thousands of dots and little circles. By covering some parts and treating others with acid again, you will get different shades of grey with a grained surface. Goya used this technique frequently. Aquatint was also used to reproduce watercolour paintings.