Scumbling is not a technique I have used very much. Because I usually paint on board which I prime to be smooth as the proverbial baby's bottom, I had assumed the dry, scrubbing in of paint wouldn't work as there is no canvas texture for it to rub off on to.
This was wrong, however.
Provided I can wait patiently for my first pass at the painting to dry, I have found even tiny paint ridges will accept a scumble nicely - and what is more I can wipe it off again if I hate it or over-do it.
The technique is very rough on brushes, but as I can't bear to throw knackered brushes away - they accumulate like so many dead flowers in jam-jars all around my room - I have lots of brushes I can use instead of my "best" ones.