From what I understand they are rubbing slurry onto the stone and then using the slurry stone to roll around on the stone. This will break down the binder in between the garnets of the slurry. Coticule garnets do not break down themselves, they are almost as hard a diamond. I am not sure how they are rubbing the slurry stone on the coticule and not releasing new slurry at the same time though...That part confuses me.

Alex also mentioned in one of his posts that he rubs a slurry stone on a dry coticule and then hones on the dry slurry, like CroX on Balsa. he then rubs the slurry stone on the hone against to mash up the slurry more and repeats.

I haven't tried this yet, but I am curious, since I like to play in the slurry.