Glazing is one of several methods of applying oil paint that are called “indirect painting”techniques. The term “indirect” simply means that the painting is built up in layers which are allowed to dry before successive layers are added. Glazing is a technique which consists of applying thin layers of transparent color over either transparent or opaque paint. Usually soft brushes are used for this process. It’s a technique which was well known as early as the Renaissance but fell out of favor in the 19th century when more direct painting methods became favored.
Indirectly painted works are composed of distinct layers of paint. Some passages are applied transparently as glazes, others applied translucently as scumbles or velaturas and others in opaque paint. All of these layers may be visible when one looks at the surface of the painting. What happens when light strikes an indirectly painted work? Here’s a diagram.
The light passes through the surface of the painting (rather than reflecting back as it does off an opaque paint surface), strikes the ground or other opaque layer, and bounces back out, creating that “glow from within” look.
When different surfaces are combined – all transparent, transparent glaze over an opaque layer, scumble over transparent, etc- all sorts of different optical effects are created. The light enters and reflects back in different ways on different parts of the painting surface.
This creates an optically complex look that just cannot be gotten any other way. Because the light travels back through the layers, it enters the eye in a more diffused state and creates both a glow and luminosity that enhances the atmospheric look of the work. Shadows look deep, transparent and mysterious, scumbles create air and atmosphere, softly covering forms, and opaque passages look even more brilliant.
But glazing isn’t just for indirect painters. It can also be combined with direct painting. A glaze can be added to darken or unify a passage in a directly painted work, to soften a transition between passages, and to add depth and luminosity to shadows.