To paint is to apply colour to a surface, such as a piece of paper or a canvas, with a brush or other implement. It's a very old kind of art. In a painting, the colour pigments can be employed in either a wet or dry form. There are a wide variety of painting materials available to artists, including watercolour, acrylic, oil, fresco, and tempera, to name just a few. Some artists choose to use sponges, knives, and airbrushes in addition to brushes to apply the material to the surface. There are a wide variety of substrates on which paintings can be created as well. Some of these include: paper and canvas; wood; glass; lacquer; ceramics; leaves; and even concrete.