This program is so cool. . . so cool.

In the process of oil painting in the non-virtual world, one can wipe away wet paint with a rag. The result is reductive, but not all the way to blank white as with the eraser tool. There is still the lingering tint of the pigment, streaky or soft tonal, on the canvas, with the tooth of the canvas still visible.

So it can be contolled as an old master device for underpainting, commonly in warm browns, using a combination between brush and rag. It works often as a monochromatic value study upon which colors can be applied with corresponding values.

In ala prima painting, it can be simply a framework of long slapdash zeroing-in strokes upon which the painter can tighten up areas of the painting, giving within the painting a range of marks, focal areas and levels of finish.

The 'paint rag' would be excuisite as a tool if you're so inclined to add it for emulating oil painting.