Applying colours in thin , transparent layers on an opaque layer is called "glazing". When you apply a transparent colour over another colour,the transparent colour visually alters the first ; the light rays mix, creating a visual colour blend. When used correctly, glazing can give great depth to a painting.
It is important to use extremely transparent media for this kind of painting, and you must allow each layer to dry thoroughly before applying the next. Glazes are usually applied in a slightly deeper value than needed and then softened back to the desired depth by wiping off paint with a soft brush, cloth , or finger.
