The German artist Gerhard Richter (1932- ) begins an abstract painting with a simple composition of wedges and arcs in primary colors and lets it dry. When he returns to the canvas he repaints it in a neutral color, concealing the original image. Then he scrapes away the top layer, allowing bits and pieces of the under-painting to show through. Richter can be seen painting by this method in the film Gerhard Richter Painting (2011), directed by Corinna Belz (http://www.imdb.com/title/tt1982113/?ref_=nv_sr_1). In the film he uses a two-handled squeegee to smear on or scrape away superficial layers, pulling it across the canvas in a smooth motion or in choppy jerks to crease the wet layers of paint. With a palette knife he hacks at the surface layer, exposing jagged blocks of color.
Cole TB. Ice (2)Gerhard Richter. JAMA. 2013;310(19):2018-2019. doi:10.1001/jama.2013.5418