Kathy McDonald on sat 4 jun 05
to bisque firing in gas kiln.?
Ron,
The cracking on the edges is not sharp . The cracks look as thought they
happened during the cooling process at one stage or another.
The ambient temperature of the glaze load
was under 100 degrees when I opened the damper during the bisque and the
pots
were cool enough to touch when I opened the glaze load.
I have wondered whether or not one of the factors might be that the kiln
(Geil 20 cu ft downdraft)
is designed without bagwalls and that the direct flame hit some of the pots
during the bisque
firing and subsequently caused uneven heating at that stage.
I used to bisque all the time in an old catenery arch downdraft with burners
in 4 corners and
bagwalls and never had the same issues with cracking so I suspect it had to
do with
the ware coming into direct contact with the flames from the burners because
they go directly up the
side walls of the kiln.
On further inspection of the firing it does seem that those pots fired in
the bisque
that were on the outside edges of shelves suffered the most cracks and
dunts.
I may try the bisque again. but I will cut some softbricks and stack them to
protect the ware
from direct contact with the flames.
Any other feedback or suggestions from those using a similair kiln are
welcomed.
I want to make the best use I can of this gas kiln until I can afford to
replace my electric kilns.
Thanks,
Kathy
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of Ron Roy
Sent: Saturday, June 04, 2005 1:03 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Dunting and warping in Glaze fire: Is there any relationship to
bisque firing in gas kiln.?
Hi Kathy,
Did the cracing happen on the way up or on the way down?
If the edges of the glaze at the crack are sharp they happened on the way
down in the glaze firing.
If they are not sharp they may have happened on the way down in the bisque
firing. Could it be the damper on your gas kiln is not closing properly?
RR
>I posted a message to the laist about a week ago asking for
>some opinions on bisque firing in the gas kiln as my electric ones are
>old and need elements replaced badly.
>
>I went ahead and bisqued about 100 pots in the gas kiln.
>
>Used cones and the DDE controller. Kept it oxidizing the whole way and
>fired very very slowly.... not more than a 50 degree per hour rise for the
>entire bisque. Clays and glazes were ones I have used for over 20 years so
>i do not believe them to be the factor.
>
>The bad news is....I fired a glaze load and almost 30% of the pots in the
>glaze load are dunted. The only difference between this load and the
dozens
>of loads that have been fired in the same kiln is the bisque firing.
>
>My question is:
>
>Should I rebisque the remaining 40 or so pots in the electric kiln and does
>anyone think this might have a chance of fixing the problem.?
>
>Do others use a gas kiln to bisque and if so what reccomendations would you
>have for me?
>
>TIA
>
>
>Kathy McDonald
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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