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wood fire with high iron clay revisited

updated fri 30 sep 11


Michael Mahan on thu 29 sep 11

We fired our Manabigama wood-fired kiln this past Monday, and we
succeeded at keeping the kiln away from a lot of reduction, hoping
this would help prevent bloating in the clay. We had very minimal
bloating, but we did reach nearly cone 12 in the front. We wanted to
keep it at cone 10. Most of the clay in the this load is my local
clay, high in iron and it tends to bloat at high temperatures and
when the kiln has a lot of reduction. I did add a small amount of a
high temperature white clay from StarWorks Ceramics to the mix.

We were very pleased with the results, and look forward to firing
more local clay in the wood kiln. It was a slow firing, maintaining a
rate of increase of 100 degrees an hour for most of the firing. The
kiln didn't seem to want to climb faster than that, even when we
tried to. Our stokes were with less wood than usual. We side stoked
in the middle of the kiln, which did create some reduction around
that area. Total firing time was 18 hours.

So, here's a list of things I think helped keep the bloating at bay:

Bisque fired everything.
Smaller stokes of wood.
Didn't seal the cracks in between bricks around the stoke hole.
Fired to a lower temperature than in the past.
Rate of temperature rise remained 100 degrees F. for most of firing.
Didn't pull the passives out.
It was an overcast day, and it's been raining much of this week.

We think we'll do more side stoking, but not put a low shelf between
the side stoking area and the back of the kiln. This seemed to keep
the side stoking flame from reaching the top of the kiln.

More pictures can be viewed at my Facebook page. If you go to my blog
at, there's a link to the page
there. Or better yet, come to our R.D. Mahan Kiln Opening and Turkey
Roast this Saturday and see the pots for yourselves while enjoying
some smoked heritage turkey, scones and leak and potato soup.

Michael Mahan

From the Ground Up