Ivor and Olive Lewis on sat 15 sep 07
Dear Eve Gallagher,
Rhodes 32 glaze is described as a High Alumina Mat. Alumina is derived =
from the Kaolin and the Felspar. Increasing the Silica content provides =
more vitreous solvent. This can hold the excess Alumina in solution =
during cooling. This would destroy the mat surface.=20
So if it is fired to full maturity which means all the ingredients have =
gone into solution, then during cooling excess Aluminiium Oxide in =
solution will be precipitated. This material has the same physical =
characteristics as Corundum, Ruby and Sapphire. It is most notable for =
its hardness, Mohs Scale 9. It is one of the natural abrasives.
Because of rapid cooling the crystals breaking through the surface are =
small and extremely abrasive. Hence the mattness. A knife will not =
scratch the glaze. The glaze removes metal from the knife. This leaves a =
trail of discolouration on the surface of the pot.
This marking might be a fact you just have to live with.
Ron Roy on tue 18 sep 07
It's not going to melt at cone 6. You will need some boron or zinc - I
think you will fire in reduction so the zinc will not help much - that
This is fairly close in ratio - fire it in a hot spot near the top of your
kiln so it will cool slow enough to recrystallize. I would recommend adding
the rutile as well.
RR revision of Rhodes 32 for cone 6 reduction.
NEPH SY............. 39.00
FORMULA & ANALYSIS
*CaO........ .44 11.96%
MnO2....... .00 .01%
*MgO........ .30 5.86%
*K2O........ .05 2.16%
*Na2O....... .22 6.53%
Fe2O3...... .00 .29%
TIO2....... .00 .07%
B2O3....... .14 4.75%
AL2O3...... .38 19.08%
SiO2....... 1.69 49.28%
P2O5....... .00 .03%
RATIO 4.39 (original is 4.33)
Let me know how it works please - RR
>If I change the Rhodes recipe #32 from:
>Will I have brought this glaze down to a ^6 ? and still be a very
>Thanks , Eric in Oceanside
15084 Little Lake Road
Ivor and Olive Lewis on tue 18 sep 07
Glad you found that information interesting.
Slowing your cooling rate will give time for crystals to grow larger and =
so the degree of roughness may increase.=20
If it is just plain steel that is causing the marks, soaking in strong =
Citric acid may remove them. But this treatment would not remove marks =
from Stainless steel.