Hamster Litter works really well, and completely burns out in the firing. I
have two kitchen tools that are fantastic. One is a roller with prongs coming
off all the way round, and the other is evenly spaces rollers that look like
plastic pizza cutters.
Another fun textural thing is to dip cheesecloth in heavy slip and drap it on
the pots. If you have a paper shredder, you can randomly press shreds into the
surface of the pot.

Linda D in TX