Your product says it is Australian bentonite, but we have both the sodium and calcium bentonite (aka Fullers Earth) here in Oz, so you would have to know which one it is.  Search sodium bentonite and calcium bentonite on these forums and there is plenty of discussion.   Have to say that in my experience/research cat litter is usually the calcium bentonite variety.  Calcium bentonite is plenty plastic, but not sure how much that will matter for slip casting? I think shrinkage will be th