Underpainting is the starting layer of paint a painter uses to cover a ground/base layer. The underpainting acts as a base layer for all the future layers of paint. Often artists will execute the underpainting in a monochromatic color scheme. This assists the artist in differentiating the tonal values for future paint layers. Grisaille and verdaccio are both examples of kinds of underpainting a person can do. The term originated from the idea that the underpainting is completed with the intent of painting it yet again (overpainting). An artist follows a method of working in layers with the paint to finish the piece. While it is true to many underpaintings are monochromatic, they do not have to be. Underpaintings can be done in multiple colors, and artists such as Jan van Eyck and Giotto both used multi-color underpainting in their work. Multi-color underpainting can be covered with future layers of paint color and be mixed optically by the human eye, thus preventing the artist from having to mix the color pigments physically and risk making the colors muddy.