John Hesselberth on mon 19 sep 11
Hi Stephani,
No need to=3D20
>=3D20
> 'scuse my goofy analogies.
That was probably the best, clearest explanation I have ever read of why =
=3D
you want to slow cool some glazes.
Regards,
John
On Sep 19, 2011, at 9:28 AM, Stephani Stephenson wrote:
> Paul wrote:
> "I just wonder what the scientific rational for slow cooling is for =3D
most
> electric glazes. Maybe one of the more scientific potters out there =3D
can
> enlighten."
>=3D20
> Paul=3D20
>=3D20
> i am not a 'scientific potter' necessarily ,but here is my =3D
understanding of
> it. The explanation is not precise, but it helps me visualize what is =3D
happening.
>=3D20
> I fire in an electric kiln and can compare a smaller, thin walled =3D
octagon
> kiln to my larger Cress with seven inch thick walls, which will take =3D
several
> days to cool down if you leave it closed. with many, but not all ,o f =3D
my
> glazes there is a decided difference.
>=3D20
> What happens is that at the top end of the firing, at the high heat, =3D
when
> the glaze is molten, liquid, and the clay is also at it's softest =3D
point,
> atoms and molecules are at the the most frenzied part of the dance. =3D
They are
> exchanging and interacting with each other faster than a busy day on =3D
Wall
> street. Bonds are breaking and getting reestablished faster than at =3D
peak
> night at Carnivale. ('scuse my goofy analogies.)
>=3D20
> Heated liquid is able to hold more elements in suspension than cooled =
=3D
liquid.
> if there are certain elements in excess, they will be swimming around =3D
freely
> in the melt, but as the liquid cools they will begin to precipitate =3D
out, and
> some will begin to form crystals.=3D20
>=3D20
> the longer you can keep everything in a fluid state while still =3D
cooling, the
> more time these elements have to form and grow crystals. people who =3D
work
> with macrocrystaline glazes enhance this process by limiting the =3D
alumina,
> for a very fluid glaze , seeding that glaze with crystals , and slow =3D
cooling
> it to enhance crystalline growth.=3D20
>=3D20
> Many of our lovely complex glaze surfaces work the same way, but not =3D
to
> that degree, due to our needs, choice of glaze materials , clay, and
> process , etc.
>=3D20
> Once the glaze cools to a more solid state, everything is more or =3D
less
> 'frozen' . at least in short term time.
>=3D20
> Those crystals, the precipitate, may look crystalline or it may just=3D2=
0=3D
> appear as one type of matte glaze, because the crystalline or
> precipitated elements act to defract light, so when we look at the =3D
glaze, we
> are looking at defracted light bouncing into the glaze and clay and
> bouncing back up to our eyes, i.e., a cloudy pond or a pond with =3D
seaweed or
> lily pad islands versus a clear pond.
>=3D20
> not all glazes will change. some stay much the same, slow cooled or =3D
not,
> because their chemical make up and relative ratios/percentages of =3D
chemicals
> vary . which is a whole line of study or experimentation in itself.
>=3D20
> That is my reading of the elephant from where i stand.
>=3D20
> Stephani Stephenson
Stephani Stephenson on mon 19 sep 11
Paul wrote:
"I just wonder what the scientific rational for slow cooling is for most
electric glazes. Maybe one of the more scientific potters out there can
enlighten."
Paul=3D20
i am not a 'scientific potter' necessarily ,but here is my understanding =
=3D
of
it. The explanation is not precise, but it helps me visualize what is hap=
=3D
pening.
I fire in an electric kiln and can compare a smaller, thin walled octago=
=3D
n
kiln to my larger Cress with seven inch thick walls, which will take seve=
=3D
ral
days to cool down if you leave it closed. with many, but not all ,o f my
glazes there is a decided difference.
What happens is that at the top end of the firing, at the high heat, when=
=3D
the glaze is molten, liquid, and the clay is also at it's softest point,
atoms and molecules are at the the most frenzied part of the dance. They =
=3D
are
exchanging and interacting with each other faster than a busy day on Wal=
=3D
l
street. Bonds are breaking and getting reestablished faster than at pea=
=3D
k
night at Carnivale. ('scuse my goofy analogies.)
Heated liquid is able to hold more elements in suspension than cooled li=
=3D
quid.
if there are certain elements in excess, they will be swimming around fre=
=3D
ely
in the melt, but as the liquid cools they will begin to precipitate out, =
=3D
and
some will begin to form crystals.=3D20
the longer you can keep everything in a fluid state while still cooling, =
=3D
the
more time these elements have to form and grow crystals. people who work=
=3D
with macrocrystaline glazes enhance this process by limiting the alumina=
=3D
,
for a very fluid glaze , seeding that glaze with crystals , and slow cool=
=3D
ing
it to enhance crystalline growth.=3D20
Many of our lovely complex glaze surfaces work the same way, but not to
that degree, due to our needs, choice of glaze materials , clay, and
process , etc.
Once the glaze cools to a more solid state, everything is more or less
'frozen' . at least in short term time.
Those crystals, the precipitate, may look crystalline or it may just=3D20
appear as one type of matte glaze, because the crystalline or
precipitated elements act to defract light, so when we look at the glaze,=
=3D
we
are looking at defracted light bouncing into the glaze and clay and
bouncing back up to our eyes, i.e., a cloudy pond or a pond with seaweed=
=3D
or
lily pad islands versus a clear pond.
not all glazes will change. some stay much the same, slow cooled or not,=
=3D
because their chemical make up and relative ratios/percentages of chemic=
=3D
als
vary . which is a whole line of study or experimentation in itself.
That is my reading of the elephant from where i stand.
Stephani Stephenson
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