Snail mused about temp increase. I see bubbles even before starting the tumbler. These could be just air displacement.
They only get slightly above room temperature.
JM I do a low bisque, around 010. The pieces are quite smooth after 8 to 24 hours with no additional grIit. Clay with grog probably wouldn't work.
After high fire they are tumbled again. The polishing after bisque eliminates the need for grit. It might speed up the polishing to use fine, or other finishing compound, but not needed. I like not having to deal with / risk getting SiO in my clay reclaim. I like to change the water occasionally.