Before: wet on wet painting with dark clouds and graded sky
After: glazing to strengthen the sky colors, and darken the bottom of the clouds, and scumbling to lighten the clouds
In the Deborah Paris Painted Sky class we are learning the indirect painting techniques of glazing and scumbling. Usually I paint in a direct manner, i.e., wet-on-wet, also called a la prima. This is the most common approach to plein air painting. In indirect painting, multiple layers of paint are used. When some of the layers are transparent or semi-transparent, you can get some wonderful effects. Here's a post by Deborah that explains how it works.
Glazing uses transparent paint layers. Scumbling is similar, but a little white or light value color is added to the glaze. Glazing darkens the existing surface, scumbling lightens it. I'm finding it very difficult to take realistic before and after pictures of this, believe me, the pink in the bottom painting is darker than that in the top painting! And, I think I'm doing the glazing properly, but my scumbling needs work.