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glaze test for marci's matt, cone 6, reduc. but fired oxidation.

updated wed 26 jul 00

 

Alisa and Claus Clausen on thu 20 jul 00


This glaze was one given by Marica Selsor May 11 in her list of cone 6 =
reduction glazes.
Thank you.
=20
I fired it on light grey, mid range stoneware, but oxidation
=20
Receipe
EPK 23
Dolomite 20
Neph. Syn. 38
Silica 4
Whiting 4
Gerstely Borate 10 =20
=20
Tests resulted in a semi mat clear which crazed. Small to large cracks =
over entire surface.
=20
Would the difference of reduction to oxidation cause this fault?
I would like to much further test this glaze and all the others she =
posted. Especially this one as=20
a base for all the coloring suggestions she lists.
=20
Best regards,
Alisa in Denmark.

Marcia Selsor on thu 20 jul 00


Dear Alisa,
Jeff Lawrence fired them in reduction with great success. I think it
crazed because it doesn't fit your clay body. I never had it craze on
our stoneware. Do you think the electric kiln cooled faster than a large
gas? That might be another reason.
Marcia

Alisa and Claus Clausen wrote:
>
> This glaze was one given by Marica Selsor May 11 in her list of cone 6 reduction glazes.
> Thank you.
>
> I fired it on light grey, mid range stoneware, but oxidation
>
> Receipe
> EPK 23
> Dolomite 20
> Neph. Syn. 38
> Silica 4
> Whiting 4
> Gerstely Borate 10
>
> Tests resulted in a semi mat clear which crazed. Small to large cracks over entire surface.
>
> Would the difference of reduction to oxidation cause this fault?
> I would like to much further test this glaze and all the others she posted. Especially this one as
> a base for all the coloring suggestions she lists.
>
> Best regards,
> Alisa in Denmark.
>
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--
Marcia Selsor
selsor@imt.net
http://www.imt.net/~mjbmls
http://www.imt.net/~mjbmls/spain99.html
http://www.silverhawk.com/ex99/selsor/welcome.html

Ron Roy on sun 23 jul 00


Hi again Alisa,

The crazing is probably related to the clay body. Fast firing or cooling
will have an effect as well. I have reformulated to lower the
expansion/contraction - I think it will still look the same - use your
local spar for the G200.

Frit 3134 - 15.0
Neph Sy - 13.0
G200 - 14.0
Dolomite - 24.0
EPK - 32.0
Silica 2.0
Total - 100.0

Ratio - 3.95 (original is 3.74)
Expansion - 534.09 (581.62)

If I am going to keep working on your glazes I will need the analysis for
your frit - the molecular formula you included is not good enough.

Let us know if it works please.

RR

>This glaze was one given by Marica Selsor May 11 in her list of cone 6
>reduction glazes.
>Thank you.
>
>I fired it on light grey, mid range stoneware, but oxidation
>
>Receipe
>EPK 23
>Dolomite 20
>Neph. Syn. 38
>Silica 4
>Whiting 4
>Gerstely Borate 10
>
>Tests resulted in a semi mat clear which crazed. Small to large cracks
>over entire surface.
>
>Would the difference of reduction to oxidation cause this fault?
>I would like to much further test this glaze and all the others she
>posted. Especially this one as
>a base for all the coloring suggestions she lists.

Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849

Jeff Lawrence on tue 25 jul 00


Hello Alisa and Marci,

I really like the surface on Marci's mat and Ohata red, but also suffered
quite a bit of delayed crazing on both. My clay was sandy and some of the
clay poked through the mat, too. I think higher viscosity with additional
epk might help that as well as bring the expansion down.

I've got some alterations calculated but haven't fired cone 6 lately. When I
do, I'll post them and the results.

Best,
Jeff

Jeff Lawrence vox: 505 753 5913
Sun Dagger Design fax: 505 753 8074
18496 US HWY 84/285 jml@sundagger.com
Espanola NM 87532 www.sundagger.com