Teri Lee on thu 8 feb 07
Hello,
=20
I'm looking at two sets of raku glaze recipes. One based on a gerstley =
borate and nepheline syenite base, the other set a on gerstley borate =
and cornwall stone base. Both use an 80-20 percentage format.=20
Does anyone know what's the difference in appearance between glazes that =
use nepheline syenite or cornwall stone? Is there a difference in =
crackle, opacity, etc. etc.?
=20
=20
Rus Sheptak on fri 9 feb 07
> Hello,
>
> I'm looking at two sets of raku glaze recipes. One based on a gerstley
> borate and nepheline syenite base, the other set a on gerstley borate and
> cornwall stone base. Both use an 80-20 percentage format.
>
> Does anyone know what's the difference in appearance between glazes that
> use nepheline syenite or cornwall stone? Is there a difference in crackle,
> opacity, etc. etc.?
>
>
You should go ahead and test both glazes on your clays and see what you find.
I did just that comparison in the Berkeley ASUC studio last year. We
tested both with clear crackle (the 80/20 base glazes) and with colorants
and tested on 3 different clays (c. 6 tan stoneware, c 6. porcelain, and
c. 10 sculpture mix). here's a capsule summary:
- both give a nice glossy surface.
- Neph. Sy. glaze crackled more reliably across all 3 clays. Cornwall
stone crackled well on the porcelain and stoneware, but not on the
sculpture mix.
- Neph Sy. does not reliably crackled when applied over a colored slip.
- Cornwall stone had visibly brighter more intense colors when colorants
were added.
- some colorants (cobalt) cause both glazes to not crackle.
rus
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