Regarding acceptable porosity of fired clay for functional ware, I talked to one of the head people at a large clay company many years ago to find a good body for cone 10, and he said it should be 2% or less.  I don't recall if he gave any reasoning.  I won't give you the names involved in case I have misremembered, but I still go by that myself.  YMMV.

Anybody else have a different answer? 

On Fri, Jan 21, 2022 at 10:34 AM Vanessa Greene <> wrote:
Any thoughts from all you experienced potters about those clays that are marketed as a wide ranging temp clay, cone 6-10…..are they really fully vitrified at cone 6? I hear very different opinions about this…..what absorption rate is necessary for functionally food safe pots?  ( continental clays B clay, Buff etc…. )
I have always fired these clays to cone 10 but some people suggest that these clays are suitable for both cone 6 and 10 firings. Thoughts?

Vanessa Greene