Eleanora Eden on wed 11 jan 06
Hi Liz and all,
If I were looking for a satin surface and worried about glaze fit I
would start with petalite as a basis for making up a glaze.
From Digitalfire: Petalite can be used to create low expansion
glazes. It is suitable for white and transparents as well because of
the low iron content. It does not present the frothing problems
sometimes associated with spodumene and helps improve brightness. One
formula suggested by Val Cushing is petalite 76.9, talc 14.2, whiting
3.4, kaolin 5.5.
I made a petalite glaze for ^1-3 that could be easily adjusted for
^6. It seems to work without crazing on several very disparate clay
bodies and always has a buttery satin sheen that seems to be
characteristic of petalite. I just looked at it with a ^6 target
formula and it is maybe a bit low in alumina but within ^6 specs
otherwise. I started with the above recipe from Val Cushing and got:
Eden's Satin Petalite glaze
23.00 Petalite
15.00 Talc
10.00 Wollastonite
5.00 Whiting
8.00 Flint
25.00 Custer Feldspar
10.00 *EPKaolin
4.00 Zinc Oxide
0.39* CaO
0.09* Li2O
0.28* MgO
0.07* K2O
0.04* Na2O
0.13* ZnO
0.23 Al2O3
2.48 SiO2
Thermal Expansion: 6.38
If anybody does try this formula I would appreciate hearing about the results.
Eleanora
Ron Roy on tue 17 jan 06
I just calculated out both glazes and want to warn everyone that the Rhodes
glaze has a very low expansion rate and would be a problem on any pottery
clay body I know of.
On the other hand - your glaze is right in the "ballpark" for a good fit on
many clay bodies - except those that that have cristobalite in them.
Spodumene is the material of choice for lowering expansion because it has
more Li2O than Petalite. Both materials are useful when used with some spar
or Neph Sy when curing crazing is the goal.
RR
>Hi Liz and all,
>
>If I were looking for a satin surface and worried about glaze fit I
>would start with petalite as a basis for making up a glaze.
>
> From Digitalfire: Petalite can be used to create low expansion
>glazes. It is suitable for white and transparents as well because of
>the low iron content. It does not present the frothing problems
>sometimes associated with spodumene and helps improve brightness. One
>formula suggested by Val Cushing is petalite 76.9, talc 14.2, whiting
>3.4, kaolin 5.5.
>
>I made a petalite glaze for ^1-3 that could be easily adjusted for
>^6. It seems to work without crazing on several very disparate clay
>bodies and always has a buttery satin sheen that seems to be
>characteristic of petalite. I just looked at it with a ^6 target
>formula and it is maybe a bit low in alumina but within ^6 specs
>otherwise. I started with the above recipe from Val Cushing and got:
>
>Eden's Satin Petalite glaze
>
>23.00 Petalite
>15.00 Talc
>10.00 Wollastonite
>5.00 Whiting
>8.00 Flint
>25.00 Custer Feldspar
>10.00 *EPKaolin
>4.00 Zinc Oxide
>
>0.39* CaO
>0.09* Li2O
>0.28* MgO
>0.07* K2O
>0.04* Na2O
>0.13* ZnO
>0.23 Al2O3
>2.48 SiO2
>Thermal Expansion: 6.38
>
>If anybody does try this formula I would appreciate hearing about the results.
>
>Eleanora
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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