Jenny Lewis on fri 3 jun 11
Hi all
I had a bit of a rummage in the archives, but can't find exactly what
I'm looking for. I use (UK) Potclays White St Thomas clay, and fire
to 1,260 centigrade (Cone 7, I think). I assumed this was a high
enough temp to vitrify the clay/glaze.
However, recently I was chucking out some flowers that had been in one
of my vases and noticed that its bottom was wet. I checked for cracks
or crazing (thank you Dinah!) and then tested a whole lot of other
pots, and they are all porous! Not huge puddles but if I fill them
with water and stand them on kitchen paper towel overnight, next
morning there are soggy bottoms and damp paper. Dammit.
I have done a couple of firings to 1,270 C, to try some different
glazes, and those pots seem ok.
I don't mind going for the higher temps in future, but just wondering
what to do with stuff I have made. I plan to refire a few, just to
see what happens. Someone I know - engineer, non-potter - suggested
coating the insides with PVA. Anyone done this?
Recently I made about a dozen vases, 2 or 3 sections stuck together,
that took me ages, so I would like to try to hang on those if poss!
Thanks in advance,
in anticipation,
in the UK
Jenny Lewis
John Hesselberth on fri 3 jun 11
On Jun 3, 2011, at 2:27 PM, Jenny Lewis wrote:
> I don't mind going for the higher temps in future, but just wondering
> what to do with stuff I have made. I plan to refire a few, just to
> see what happens. Someone I know - engineer, non-potter - suggested
> coating the insides with PVA. Anyone done this?
Hi Jenny,
Try refiring, but that is always a bit problematic. You may get some =3D
breakage particularly if any of the pots have held water. If they have =3D
held water, go very, very slowly in the early stages of your firing.
My personal view is that you should never count on glaze or other =3D
coatings for water-proofness. Sufficiently vitrified clay is the best =3D
answer. Even some non-crazed glazes will pass water on a porous body. A =3D
polymeric coating will sooner or later come off when you least expect it =
=3D
to. I always aim for 2% or less unglazed water absorption using the =3D
fairly standard water absorption test.
If you are ever tempted to make oil lamps be even more careful. Lamp oil =
=3D
is even harder to keep in a pot than water is.
Regards,
John
paul gerhold on sat 4 jun 11
Jenny
About thirty years ago when I was just starting I coated the inside of a po=
t
with fiberglass resin to make it hold water. It was not glazed on the
inside if that matters. It still holds water.
Paul
On Fri, Jun 3, 2011 at 2:27 PM, Jenny Lewis
wrote:
> Hi all
>
> I had a bit of a rummage in the archives, but can't find exactly what
> I'm looking for. I use (UK) Potclays White St Thomas clay, and fire
> to 1,260 centigrade (Cone 7, I think). I assumed this was a high
> enough temp to vitrify the clay/glaze.
>
> However, recently I was chucking out some flowers that had been in one
> of my vases and noticed that its bottom was wet. I checked for cracks
> or crazing (thank you Dinah!) and then tested a whole lot of other
> pots, and they are all porous! Not huge puddles but if I fill them
> with water and stand them on kitchen paper towel overnight, next
> morning there are soggy bottoms and damp paper. Dammit.
>
> I have done a couple of firings to 1,270 C, to try some different
> glazes, and those pots seem ok.
>
> I don't mind going for the higher temps in future, but just wondering
> what to do with stuff I have made. I plan to refire a few, just to
> see what happens. Someone I know - engineer, non-potter - suggested
> coating the insides with PVA. Anyone done this?
>
> Recently I made about a dozen vases, 2 or 3 sections stuck together,
> that took me ages, so I would like to try to hang on those if poss!
>
> Thanks in advance,
> in anticipation,
> in the UK
>
> Jenny Lewis
>
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