chiaroscuro. Washes,  stipple  or dotting effects, and "surface tone" in printmaking are other techniques. http://en.wikipedia.org/wiki/Acrylic_paint Acrylic paint is fast drying paint containing pigment suspension in acrylic polymer emulsion . Acrylic paints can be diluted with water, but become water-resistant when dry. Depending on how much the paint is diluted (with water)