Glaze (painting technique)
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A glaze in painting refers to a layer of paint, thinned with a medium, so as to become somewhat transparent. A glaze changes the color cast or texture (gloss or matte, for instance) of the surface. Drying time depends on the amount of medium used in the glaze; a higher ratio of medium to paint (producing a very thin, transparent glaze) decreases drying time, while unadulterated oil paint takes the longest to dry.
A traditional oil painting begins with a grisaille in a gray or yellow ochre, as a monochromatic version of the finished piece. When this is dry, the painter begins to add layers of glaze in different colors, letting each layer dry before adding the next one. Since the layers are all somewhat transparent, the result is a combination of the colors, creating a final hue as if the painter has simply mixed the colors. The benefit of glazing is that not only does it afford the painter more control over the evolution of the painting, but it also creates a luminescent, translucent surface, with certain layers appearing to show through. Many artists consider this an important aspect to the vitality of a piece.
As glazing darkens a painting (similar to the way a color gel can dim a light), painters often repeatedly glaze surfaces that they want to recede into the canvas, such as a background wall or figure. Mixing a glaze with a small amount of white allows the painter to maintain the intensity of a highlight. Many oil paintings can have anywhere between three and thirty layers of glaze.
When the technique is used for wall glazing, the entire surface is covered, often showing traces of texture (French brush, parchment, striae, rag rolling). Either oil-based or water-based materials are used for glazing walls, depending upon the desired effect. Kerosene or linseed oil may be used to extend the "open" or working time of oil-based glazes. Water-based glazes are sometimes thinned with glycerin or another wetting agent to extend the working time. In general, water glazes are best suited to rougher textures where overlaps of color are acceptable.
Glaze is also used in cabinet, furniture, and faux finishing.
Scumble is a technique similar to glazing, except that the coating is opaque. It is normally quite difficult to identify if a painter has used 'scumble' on his or her work.