mel jacobson on sun 11 sep 11
Mel -
I don't have the recipe for Ron Roy's Black magic Cone 10 glaze - so I'm
shooting from the hip - I'm assuming this is a high iron glaze, in the tenm=
oku
family.
In that case I'm playing with such a glaze right now, and have seen this
before -
slow downfire in certain temperature regions promotes the rust red. The
temperature window in which slow cooling will cause the rust red color depe=
nds
on the glaze composition (and I'd expect also the maturing temperature of t=
he
glaze).
In a large fuel burning kiln I can easily imagine that there might be areas=
of
the kiln that hold their temperature longer. I would expect variations in
reduction in a fuel burning kiln to be relevant as well.
Here is the firing profile - is cone 6 by the cones - its 25 deg F an hour
down from 1700 to 1650, and an hour hold at 1650.
1. 150 deg F hr/ 200 deg F / hold 1 hr
2. 400 deg F hr/ 1949 deg F
3. 120 deg F hr/ 2200 deg F / hold 20 min
4. 300 deg F hr/ 1700 deg F
5. 25 deg F hr/ 1650 deg F / hold 1 hr
Here is the glaze:
si_3_4
Ball_Clay 15
Bentonite 3
G_200_Feldspar 9
Lithium_Carbonate 6
Red_Iron_Oxide 14
Silica 28
Unispar 10
Whiting 15
si_3_4
K2O 0.0623 Al2O3 0.3027 SiO2 3.0884
Na2O 0.0631 B2O3 0.0000 P2O5 0.0000
Li2O 0.2965 Fe2O3 0.3267 ZrO2 0.0000
CaO 0.5669 TiO2 0.0082
MgO 0.0114 SnO2 0.0000
SrO 0.0000
ZnO 0.0000
BaO 0.0000
A 100 gram batch of
si_3_4
has 0.273921 moles of base.
The Silica Alumina Ratio =3D 10.2023
you can pass this info to Bryan -
Carol
from: minnetonka, mn
website: http://www.visi.com/~melpots/
clayart link: http://www.visi.com/~melpots/clayart.html
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