5 Ambient occlusion
This is generally a 3D term. Put simply, it’s the innermost area of the painted object where it’s darkened by shadow. I use a Clipping layer with a Multiply setting to start painting in shadows (not cast shadows) in areas where there’s a recess: for example, the fold of the eye, the mouth or the clothing. I use black and set the layer’s Opacity to between 60 and 70 per cent.