Glazing in oil painting is primarily used for what purpose?

Glazing in oil painting is a technique that involves applying a transparent layer of colored paint over a dry layer of paint. This method is primarily used to achieve depth and richness in color. By layering glazes, artists can create complex color interactions that enhance luminosity and create a sense of three-dimensionality. The transparent nature of the glaze allows the underlying layers to show through, producing a vibrant, glowing effect that can't be achieved with opaque paints alone.

The other options presented do not encapsulate the primary function of glazing. While a monochrome effect can be achieved through other techniques, the richness of color that glazing provides is distinct and more nuanced. Lightening a color layer typically involves adding white or a lighter color rather than glazing. Moreover, mixing colors directly on the palette does not involve layering and transparency, which are central to glazing techniques. Thus, the purpose of glazing is strongly linked to enhancing the depth and richness of color in painting.