the cat lady on thu 1 oct 98
I took the following glaze off clayart about 2 years ago.
I've since switched claybodies (one that fires a tad higher -
both are rated ^10, but the new body doesn't slump at 10 the
way the old body did). I am currently using Tuckers ^10
Smoothstone (old body was Plainsman H550) if this is of any
help.
15.2 Silica
38 Custer Spar
21 Whiting
20.2 EPK
4.1 Titanium Diox.
1.5 Cobalt Carb (except I use silicate 'cause that's what I got)
I glazed 3 Cafe au Lait cups at the same time, fired in the same
oxidation (electric) firing. 1 is perfect. 2 bubbled (small bubbles
that "snap" when you run your finger over them). I heated the 2 cups
to 250F and re-glazed and re-fired. Larger bubbles/big pinholes.
The saucers are fine except where glaze has dripped on itself
(so too thick is no good). The cups are thrown and trimmed thinly.
Other glazes on these cups work fine.
I bisque very slowly to 06 in the sitter. All pieces are wiped prior
to glazing and I use latex gloves.
2 notes of interest - this glaze was mixed about a year ago (large
batch) and seems to get worse as it gets older....and it has developed
a rather nasty odor. Is it possible that this glaze is just too old?
The glaze breaks green where thin and on edges. I just love it. Can
someone help?
Many, many TIA
sam - alias the cat lady
Melbourne, Ontario
SW Ontario CANADA
http://www.geocities.com/paris/3110
scuttell@odyssey.on.ca
"Thousands of years ago, cats were worshipped as gods.
Cats have never forgotten this."
Farshad Barman on tue 6 oct 98
To The Cat Lady: I had the same problem with a low fire glaze that
continued for a whole year and reduced my sales. After doing quite a lot of
experiments, I found that this kind of bubbling is due to the glaze boiling
at its maturation temperature. The glaze did this on some clays and not on
others. I also found that the problem was because I had switched to mesh 400
silica instead of mesh 325 that I was using before. The finer mesh (400)
melts at a lower temperature and causes this kind of bubbling.
Try this: Test the glaze with mesh 200 and 325 silica. If this does not
work, keep the courser silica ( 200 or 325) and reduce whiting (which is a
flux) by 3% and increase EPK by 3%. This will make the glaze mature at a
slightly higher temperature and perhaps eliminate this nasty bubbling.
Good Luck
Farshad Barman
Portland, Oregon
At 10:07 AM 10/1/98 EDT, you wrote:
>----------------------------Original message----------------------------
>I took the following glaze off clayart about 2 years ago.
>I've since switched claybodies (one that fires a tad higher -
>both are rated ^10, but the new body doesn't slump at 10 the
>way the old body did). I am currently using Tuckers ^10
>Smoothstone (old body was Plainsman H550) if this is of any
>help.
>
>15.2 Silica
>38 Custer Spar
>21 Whiting
>20.2 EPK
> 4.1 Titanium Diox.
> 1.5 Cobalt Carb (except I use silicate 'cause that's what I got)
>
>I glazed 3 Cafe au Lait cups at the same time, fired in the same
>oxidation (electric) firing. 1 is perfect. 2 bubbled (small bubbles
>that "snap" when you run your finger over them). I heated the 2 cups
>to 250F and re-glazed and re-fired. Larger bubbles/big pinholes.
>
>The saucers are fine except where glaze has dripped on itself
>(so too thick is no good). The cups are thrown and trimmed thinly.
>Other glazes on these cups work fine.
>
>I bisque very slowly to 06 in the sitter. All pieces are wiped prior
>to glazing and I use latex gloves.
>
>2 notes of interest - this glaze was mixed about a year ago (large
>batch) and seems to get worse as it gets older....and it has developed
>a rather nasty odor. Is it possible that this glaze is just too old?
>
>The glaze breaks green where thin and on edges. I just love it. Can
>someone help?
>
>Many, many TIA
>
>sam - alias the cat lady
>Melbourne, Ontario
>SW Ontario CANADA
>http://www.geocities.com/paris/3110
>scuttell@odyssey.on.ca
>
>"Thousands of years ago, cats were worshipped as gods.
> Cats have never forgotten this."
>
>
Ron Roy on tue 6 oct 98
Hi Sam,
I don't know why this is happening but here are two versions adjusted #1
has more Alumina and more silica - and the second melts more - had to use a
bit of boron to keep the expansion in the same area. I've kept the
expansion close to the original in both.
melts a bit less
-----------------
SILICA.............. 15.00
CUSTER SPAR......... 49.00
WHITING............. 19.00
EPK................. 17.00
TIO2................ 4.00
coblt silicate...... 1.50
----------
105.50
FORMULA & ANALYSIS
------------------
*CaO........ .71 11.45%
*MgO........ .01 .07%
*K2O........ .20 5.39%
*Na2O....... .09 1.60%
Fe2O3...... .01 .24%
TIO2....... .19 4.36%
AL2O3...... .54 15.91%
SiO2....... 3.52 60.97%
P2O5....... .00 .02%
RATIO 6.52 (org is 6.12)
EXPAN 565.19 (org is 561.64)
WEIGHT 346.20
Melts more.
-----------------
SILICA.............. 14.00
F3134............... 5.00
CUSTER SPAR......... 40.00
WHITING............. 20.00
EPK................. 21.00
TIO2................ 4.10
coblt silicate...... 1.50
----------
105.60
FORMULA & ANALYSIS
------------------
*CaO........ .71 13.23%
*MgO........ .01 .08%
*K2O........ .14 4.47%
*Na2O....... .09 1.88%
Fe2O3...... .00 .26%
TIO2....... .17 4.52%
*B2O3....... .05 1.25%
AL2O3...... .47 16.01%
SiO2....... 2.91 58.26%
P2O5....... .00 .03%
RATIO 6.19
EXPAN 562.82
WEIGHT 299.72
All three are probably durable - although the last one (melts more) is a
little short of SiO2 at cone 10.
Hope this gives us some clues about why the bubbles are there - I don't see
anything in your original that would deteriorate with time.
>----------------------------Original message----------------------------
>
>15.2 Silica
>38 Custer Spar
>21 Whiting
>20.2 EPK
> 4.1 Titanium Diox.
> 1.5 Cobalt Carb (except I use silicate 'cause that's what I got)
>
>I glazed 3 Cafe au Lait cups at the same time, fired in the same
>oxidation (electric) firing. 1 is perfect. 2 bubbled (small bubbles
>that "snap" when you run your finger over them). I heated the 2 cups
>to 250F and re-glazed and re-fired. Larger bubbles/big pinholes.
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
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