Gesso is a milky white liquid ground made of an acrylic resin emulsion medium combined with an extender pigment such as titanium white and calcium carbonate. It is mainly used to coat substrates, fix paint and supplement coloring. Due to its strong concealing properties, it can also be used as a coloring material in much the same way as paint. It is possible to paint over the top of gesso with acrylic paint, oil paint and watercolor. Originally, the plaster surface on which tempera paintings were drawn was referred to as “gesso” in Italian. It later became a term for ground in general, including ground chalk, and today it is used in reference to this acrylic white ground.
It is commonly used by applying several layers of this undiluted liquid, or a solution made by adding around 20% water, in various directions with a brush or roller. By applying repeatedly in thin layers rather than applying a thick layer in one go, a sturdy white base of a matte texture can be created, which can also be sanded smooth. As a precaution, gesso should not be used over an oil canvas or oil paint. Moreover, if the substrate is highly absorbent, it must be coated with an acrylic medium, etc.
Colored gesso is available in addition to the basic white gesso. A colored base can also be created by mixing it with acrylic paint. Furthermore, a base with various surface textures can be produced by using extender pigments of differing particle size. Gesso can be purchased at general art stores.