Edward Cowell on thu 11 nov 99
Anyone out there who can help me with a problem with a Cone 6 Celedon I am
testing. Crazing appears on the inside of a mug, bowl, etc., but not on
the outside. Can the recipe be altered?
Birke's Celedon
Pot. Feldspar 58
Whiting 17
Flint 14
Ball Clay 6
Zinc Oxide 5
Add - Copper Ox. 1
Laurie Cowell,
Waterloo, Ontario, Canada
Cindy Strnad, Earthen Vessels Pottery on fri 12 nov 99
Laurie,
I'm a neophyte, so be warned. According to my Insight software, your glaze
falls within normal limits for oxides and such, and should be safe if it
only fits your clay body. The expansion, however, is 8.09, which is a little
high. You can increase the flint, or decrease the feldspar (I calculated
with Custer spar), or both. This is likely to alter the look of your glaze,
but it also lowers your expansion. Increasing the flint makes the largest
difference the fastest (and also doesn't add any other incidental oxides),
so if it were me, I'd start with that. Increasing the flint by 10 will lower
your expansion to 7.69, which may be enough.
Cindy Strnad
Earthen Vessels Pottery
Custer, SD
Craig Martell on fri 12 nov 99
At 05:09 PM 11/11/1999 -0500, you wrote:
>----------------------------Original message----------------------------
>Anyone out there who can help me with a problem with a Cone 6 Celedon I am
>testing. Crazing appears on the inside of a mug, bowl, etc., but not on
>the outside. Can the recipe be altered?
>Birke's Celedon
>Pot. Feldspar 58
>Whiting 17
>Flint 14
>Ball Clay 6
>Zinc Oxide 5
>Add - Copper Ox. 1
Hi:
You might give this adjustment a shot. I've lowered the expansion of the
glaze a bit. The silica/alumina ratio has changed somewhat too but this
might work ok for you. I raised the silica to the upper limit for cone 3-7
glazes. It's all below. Let us know if this works better for you.
Birke's celedon adjustment
custer feldspar..... 52.02 52.02%
whiting............. 15.25 15.25%
zinc oxide.......... 4.48 4.48%
om #4 ball clay..... 5.38 5.38%
silica.............. 22.87 22.87%
========
100.00
CaO 0.53* 9.42%
MgO 0.00* 0.02%
K2O 0.20* 5.83%
Na2O 0.08* 1.65%
ZnO 0.19* 4.84%
TiO2 0.00 0.07%
Al2O3 0.35 11.37%
SiO2 3.50 66.66%
Fe2O3 0.00 0.13%
Cost/kg 0.68
Si:Al 9.95
SiB:Al 9.95
Expan 7.50
regards, Craig Martell in Oregon
Stephen Mills on fri 12 nov 99
Might this not be the inside of the pot getting a bit hotter then the
outside? I've observed this effect in a number of situations, most
obviously in a biscuit firing, when it has been quite plain that the
inside of a container has got a greater amount of heatwork than the
outside resulting in seriously lower porosity. As Celadons are sensitive
beasts at the best of time, and in my experience prone to crazing if
overfired, it might not be the recipe that's at fault.
Steve
Bath
UK
In message , Edward Cowell writes
>----------------------------Original message----------------------------
>Anyone out there who can help me with a problem with a Cone 6 Celedon I am
>testing. Crazing appears on the inside of a mug, bowl, etc., but not on
>the outside. Can the recipe be altered?
>
>Birke's Celedon
>
>Pot. Feldspar 58
>
>Whiting 17
>
>Flint 14
>
>Ball Clay 6
>
>Zinc Oxide 5
>
>Add - Copper Ox. 1
>
>Laurie Cowell,
>Waterloo, Ontario, Canada
>
--
Steve Mills
Bath
UK
home e-mail: stevemills@mudslinger.demon.co.uk
work e-mail: stevemills@bathpotters.demon.co.uk
own website: http://www.mudslinger.demon.co.uk
BPS website: http://www.bathpotters.demon.co.uk
Tel: **44 (0)1225 311699
Fax: **44 (0)870 0526466
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