Depends on how it looks when you get it to size. If it has open pores from exposed marrow, soak it down with ca till it's smooth, and polish. if it's got lots of deep bark left on it, I usually just sand to about 600 and buff. In between, is well, in between. You don't want to get too much ca in the bark, as it won't come out, but you don't want open marrow exposed. That's what makes it fun to turn (well, that and drilling it)
but definitely don't breath it.