judy, whatever you add to the clay itself once the pot is made, comes out as thick as you want it to.
make slip as thin or as thick as you decide.
put as many layers of underglaze over the clay as you decide.
cut into the clay as deeply as you decide.
the beauty and the problem with all this is that it is your responsibility to do what will work to produce the result you desire. i am still having problems understanding the question. i hope i have not confused you.