Steve Dalton on mon 29 apr 02
on 4/27/02 9:33 PM, Ron Roy at ronroy@TOTAL.NET wrote:
> There is something that can go very wrong with bodies that have more than
a
> little iron in them.
>
> You must not reduce the iron as it can result in black coring - in other
> words - over vitrified clay due to reduced iron oxide.
>
> Best is to make sure there is lots of free oxygen - certainly no reduction
> - and not too fast from 700C to the end.
>
> You don't find out till you glaze fire - so if you get bloating - it may
be
> the bisque firing - and it can happen in electric kilns as well.
>
> 9 hours seems fast to me but much depends on how thick the clay is, how
> much carbon is in the clay - and it can vary from batch to batch - and how
> much iron is present. If the ware is stacked tightly and nested - you need
> to be extra careful.
>
> RR
Ron and others,
Ron, you're bursting my bubble! I watched my Oxyprobe very carefully to
make sure I was only in oxidation all the way up to temp. I was at the low
end on the scale, no where near the slightest amount of reduction. I was
also very careful, I hope, on how fast the firing went. Like I said before,
everything was bone dry when loaded and I made sure again before I lit off
the burners. I even slowed way down and held 07 for about an hour before
shutting everything off. 9 hours does seem fast, I'm thinking of taking the
next one(Tuesday) for 12-14 hours.
From what I can tell, everything turned out. I lost nothing due to
explosions, but like you said I won't know more until I glaze fire.
--
Steve Dalton
Clear Creek Pottery
Snohomish, Wa
sdpotter@gte.net
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