Wendy Moore on sat 8 nov 97
Greetings ...
A friend of mine has a problem with a glaze that I would also
like to use but.... it bubbles where it becomes thick, those tiny
little annoying bubbles; i.e. the bottoms of bowls, under the lips of
pitchers or vases, around rims of jars, etc. This is a fake ash glaze
that webs beautifully when applied thin on the grolleg porcelain body
that we use. (See recipe below) When Annette first adopted the glaze
she was in Chicago and it worked beautifully. When she moved to
Michigan and began working and firing at Pewabic and now at Henry Ford
Community College, the bubbles have appeared.
These bubbles do not disappear when ground down and refired. We
suspect the calcium carbonate and are beginning testing to adjust it. I
thought someone out there may have done similar testing and could get us
on our way. Other variables that may be affecting it are:
1. Is it fired too hot? ^10 in the 3:00 position
2. Could it need to bisqued higher? We bisque at ^06 because of
multiple clay bodies in the bisque kilns.
3. Could it be fired to fast? Geil Downdraft fired 2 burners over
night to ^012 at 9am. All six burners lit for reduction for 1/2 hour. 1
hour in neutral atmosphere to ^2, reduction for 1/2 hour , 3 hours to
^9, fired in neutral kiln to kiln off at ^10 in the 3:00 position.
Cooled in mild reduction til next day at noon.
4. Is there too much calcium carbonate causing gas bubbles?
Fake Ash ^10 Reduction
Custer spar 25.1
Whiting 12.0
Flint 6.6
Kaolin (EPK) 27.8
Dolomite 29.6
----
Rutile 6% for a warm creamy grey
---
RIO 2.5% for a rich yellow
Rutile 6%
---
Titanium Dioxide 4% for the white on white effect.
Any revalations from the glaze gurus out there would be greatly
appreciated. Meanwhile we test, and test, and test.........
TIA
Wendy Moore, the Apron Lady
wendym@globalbiz.net
"the cat lady (by way of the cat lady on sun 9 nov 97
When she moved to
>Michigan and began working and firing at Pewabic and now at Henry Ford
>Community College, the bubbles have appeared.
> These bubbles do not disappear when ground down and refired. We
>suspect the calcium carbonate and are beginning testing to adjust it. I
>thought someone out there may have done similar testing and could get us
>on our way. Other variables that may be affecting it are:
>Fake Ash ^10 Reduction
>
>Custer spar 25.1
>Whiting 12.0
>Flint 6.6
>Kaolin (EPK) 27.8
>Dolomite 29.6
>----
>Rutile 6% for a warm creamy grey
>---
>RIO 2.5% for a rich yellow
>Rutile 6%
>---
>Titanium Dioxide 4% for the white on white effect.
>
>
I'm no glaze guru, but there has been lengthy discussion re:
rutile bubbling problems.
If all else is the same, I would suggest dropping the rutile and
testing the "white on white" to check for bubbles. If no problem
then you have your culprit.
Ron Roy on tue 11 nov 97
This can happen when the bisque firing is not in strict oxidation between
700C and 900C and/or the bisque firing is too fast. Any fireclay in your
body? Maybe changing kilns has something to do with it.
>----------------------------Original message----------------------------
> When she moved to
>>Michigan and began working and firing at Pewabic and now at Henry Ford
>>Community College, the bubbles have appeared.
>> These bubbles do not disappear when ground down and refired. We
>>suspect the calcium carbonate and are beginning testing to adjust it. I
>>thought someone out there may have done similar testing and could get us
>>on our way. Other variables that may be affecting it are:
>
>>Fake Ash ^10 Reduction
>>
>>Custer spar 25.1
>>Whiting 12.0
>>Flint 6.6
>>Kaolin (EPK) 27.8
>>Dolomite 29.6
>>----
>>Rutile 6% for a warm creamy grey
>>---
>>RIO 2.5% for a rich yellow
>>Rutile 6%
>>---
>>Titanium Dioxide 4% for the white on white effect.
>>
>>
>I'm no glaze guru, but there has been lengthy discussion re:
>rutile bubbling problems.
>
>If all else is the same, I would suggest dropping the rutile and
>testing the "white on white" to check for bubbles. If no problem
>then you have your culprit.
Ron Roy
93 Pegasus Trail
Scarborough,Canada
M1G 3N8
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
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