The impasto painting technique involves varying the thickness and texture of paint on the canvas. This results in paintings that offer an exciting emotional response that is quite different from artwork with a more uniform application of paint. If well done, the subject of a piece of art will almost appear to leap out of its frame.
Some of the old Masters like Rembrandt and Hals, employed impasto techniques to selectively add depth and emphasis to specific areas of a painting such as the folds in clothing or wrinkles in skin. Monet used a widely variable thickness of paint to increase excitement and therefore hold and direct the eye of the observer. Van Gough utilized these techniques to evoke certain emotions.
Oil and acrylic paints dominate impasto for the simple reason that straight out of the tube they are already very thick. Their viscosity naturally allows the paint to stand out from the surface. Simply put, the more paint applied the more it raises off the canvas. Other types of paints like watercolors can be used but require a thickening agent.
The painting surface needs to be somewhat rigid and non porous. If traditional canvas is used then it must be tightly stretched on its wood frame and coated with several layers of Gesso or toned thoroughly with oil paint. Since any stretching or bending of the surface can cause the paint to eventually crack, an extremely rigid Masonite board is often used.
Because creating texture is the name of the game with impasto painting techniques, it is necessary for the artist to develop many different stroke styles. Also a wide range of brushes and knives are employed for unique effects. Some painters have been known to raid the kitchen for utensils that may yield unusual textures.