Although the earliest English use of scumbling was in the 18th century, the technique dates to three centuries earlier and Dutch painter van Eyck. Since then, many artists have scumbled to add form and luminescence to their works. In Europe and the United States, these painters include Sandro Botticelli, El Greco, Rembrandt Harmensz van Rijn, Jacques-Louis David, Paul Klee, Georges Braque, Amedeo Modigliani, Chaïm Soutine, Milton Avery, Francis Bacon and Pierre Soulages.
To contrast a canvas underpainting, artists choose an opaque or semi-opaque hue, often light over dark or complementary colors. They load their painting tool with diluted oil or acrylic paint, wipe the excess on a rag to remove most of the moisture and gradually layer a thin film of irregular color, lightly scrubbing the tool across the crests of the canvas weave in circular or back-and-forth motions. Technical variation involves experimenting with color, viscosity, surface, implement, angle and pressure.
Paintbrushes, palette knives, sponges, rags and hands are used to scumble. A soft brush works for gradations, yet a beautiful sable shouldn't be wasted. An old bristle or synthetic brush scrubs better, enhancing the underpainting's irregularities. A palette knife produces heavier texture, whereas sponges and lint-free rags are subtler. Similarly, fingertips and palms allow gentler pressure and gentler results. Additionally, claylike pigments enhance a painting's surface. As with any painting technique, experimenting with tools produces interesting results.
Because effects develop gradually, scumbling is mastered easily. It alters the underpainting without obliterating it, allowing for rich overlays and subtle combinations within painted gradations, atmospheres and foregrounds. In "The Encyclopedia of Oil Painting Techniques," Jeremy Galton wrote, "In skillful hands, scumbling can create some of the most magical effects in a painting, giving a veil-like impression." Due to the pigments' reflective qualities, scumbled areas often appear luminous, creating beautiful fog, vibrant skin and luxurious fabric.
Scumbling is ineffective on non-canvas surfaces. Also, colors must contrast or complement. Whether an artist intends a pearled opalescence or a smoky smudge, overblending can flatten or oxidize her efforts; correct requires scumbling the underlayer color on top or removing the still-wet top layer with a soft clean rag moistened with water or turpentine. Corrected mistakes might contribute to a painting's complexity.