The painting technique that applies thin, transparent layers to build depth is glazing.
In glazing, each translucent layer modifies the color and value beneath it rather than completely covering it. In oil painting, light can pass through the glaze, reflect from the lighter underpainting, and return through the colored film, creating a luminous effect.
Glazes were especially important to Renaissance and Baroque painters, who used them to model skin, deepen shadows, enrich fabrics, and create atmospheric transitions. Because each layer is allowed to dry before the next is added, the colors blend optically rather than being physically mixed on the palette.
A common mix-up is scumbling. Scumbling also uses a thin layer, but the paint is generally opaque and is dragged lightly across the surface so that the layer below remains visible. Impasto is the opposite in appearance: it uses thick, textured paint.