I hate "unsolved" problems that so:
first of all, carbon black is a term used for a carbon surface which is made form tiny carbon particles in order to increase the active surface for a reaction that take place there
Often some of the particles are not totally bonded with the rest of the carbon black, and with slight movement you can separate them from the C.
If the C black is "washed" that means that these particles are already separated or washed from the C surface.