David Hendley gave a good answer. To me, the most important consideration is that maturation of clay and glazes depends on both temperature and duration. So if you glaze-fire again to the same cone, it is the like increasing the duration of the firing beyond the normal maturation point. Thus, you end up with slightly overfired wares, possibly over-vitrified, more brittle, with lower thermal-shock-resistance, as David said.
A cone 8-11 claybody fired to cone-9 both times would stand up to refiring just fine. A cone 8-11 claybody fired to cone-11 both times would almost certainly be over-vitrified.
Potter, Writer, Teacher
Chapel Hill, NC
From: Clayart <email@example.com> On Behalf Of Barry Salaberry
Sent: Sunday, April 24, 2022 2:03 PM
Subject: [Clayart] re-firing
I wonder if re-firing makes the pots more brittle that convention would serve?
Would a dilatometer measurement of both provide less anecdotal survey?
Does cristobalite increase or decrease with that re-fire?
Is the pot which has been re-fired more subject to thermal shock?
Does it affect glaze fit?
Questions surface when we enter a new cave, but light does provide clarity one hopes.
"Hope is the thing with feathers
That perches in the soul
And sings tunes without the words
And never stops - at all!"
-------------- next part --------------
An HTML attachment was scrubbed...