Heather Pedersen on mon 1 feb 10
Good morning!
On Saturday I completed my first cone 10 firing in my new kiln. The
glaze was cone 10 clear from Clay Planet, and the clay was Southern
Ice Porcelain, previously bisqued to cone 06.
Results:
Didn't have any breakages or crazing: Yay!
However, I do have hundreds of tiny little bubbles suspended in the
glaze making everything look a bit washed out. The bubbles were
largest on my mishima pieces for some reason.
My guess is that I needed to hold at top temp for longer? i.e. that
the glaze needed more time to get the volatiles out, or maybe I need
to add a slight amount of flux to the glaze because I am only firing
to 2300F (even though I am soaking a long time). Any other
suggestions or comments?
My recipe:
1) Ramp at full power to 200F, hold for 10 minutes
2) Ramp at full power to 2300F (I had thought it could do 2350F, but
it turned out it couldn't. Good thing I was using a cone)
3) Hold until the cone "goes down": The tip of the cone 10 self
supporting cone was 3/16" above its base [5mm]. That took 1 hour and
10 minutes.
All told, the firing took 3 hours from start to cone down, and then 2
more hours to cool (opened peep hole, then door open 1" at 1500F, then
opened all the way at 575F)
Regards,
Heather Pedersen
Lee Love on mon 1 feb 10
Slipped surfaces will bubble and/or pinhole more often than the bare
clay body. You might try sponging the inside of the pot (usually)
and/or the outside slipped areas to cut down on this.
--
Lee, a Mashiko potter in Minneapolis
http://mashikopots.blogspot.com/
=3D93Observe the wonders as they occur around you. Don't claim them. Feel
the artistry moving through and be silent.=3D94 --Rumi
KATHI LESUEUR on mon 1 feb 10
One of the things you might check into while trying for fast firings
is what effect fast firing has on the life of your kiln. Years ago I
had a conversation with the owner of Crusader Kilns. He cautioned
against rapid firings telling me that the stress on the brick would
significantly shorten the life of the kiln. You might want to contact
the manufacturer for their opinion.
KATHI LESUEUR
http://www.lesueurclaywork.com
On Feb 1, 2010, at 3:18 PM, Heather Pedersen wrote:
> Good morning!
>
> On Saturday I completed my first cone 10 firing in my new kiln. The
> glaze was cone 10 clear from Clay Planet, and the clay was Southern
> Ice Porcelain, previously bisqued to cone 06.
>
> Results:
> Didn't have any breakages or crazing: Yay!
> However, I do have hundreds of tiny little bubbles suspended in the
> glaze making everything look a bit washed out. The bubbles were
> largest on my mishima pieces for some reason.
>
ivor & olive lewis on tue 2 feb 10
Dear Heather Pedersen,
The presence of Red Iron oxide as a residual contaminant can be a cause of
bubbles when a glaze if fired above cone 8. RIO decomposes freely at
atmospheric pressure when the temperature rises above about 1400 deg C.
Iron oxide may be present as an accessory mineral in some rocks from which
Felspars are extracted.
You may need to run trials to ascertain how long to maintain your top
temperature for the gas (Oxygen) to dissipate.
Regards,
Ivor Lewis,
Redhill,
South Australia
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