Wednesday, March 30, 2011

Rich Reduction at cone 7-8

Here is a couple of pieces from my last firing. Using my latest method of firing this kiln (see last post) I can now really push heavy reduction throughout the kiln. All pieces are from a mixture of clays using a lot of grog for temper, and have a good coat of an iron oxide wash.

The iron and heavy reduction gives a nice grey sheen to the pieces.  This is a great unglazed look for a pine or juniper. Here is a commissioned piece for a beautiful pine:

I enjoyed designing this pot, with the tree design in mind. Here is the other side:

I also fired some other bonsai forms.  Here is a medium nanban, perfect for a literati style evergreen tree:

Here is a commissioned nanban, very rustic, measuring 17 inches across.  It was quite a lot of work being coil built, and it required a lot of pinching!

Here is the bottom; a double ringed foot for support and five drainage holes and tie down holes:

All in all it was a very successful firing with all cone packs looking identical.  I am quite fortunate to the the kiln gods looking over my creations. Enjoy!

Wednesday, March 16, 2011

Fine tuned firings

This post is a shout out to my clay buds. For all of us that have gone down the road of uncertainty, from firing in a SAFE electric kiln to jumping in full steam ahead into the world of atmospheric/gas, we know it is a challenging uphill climb. I knew that I was going to be flying blind at times, but I also knew through previous experiences that the harder the challenge, the higher the rate of failure, the more I would be able to learn and grow. So this post is about the trials and tribulations of firing one of the most troublesome kilns on the market today, the Olympic Torchbearer kiln.

What problems did I have you may ask?  Well, overfiring, underfiring, and not being able to monitior things like gas pressure and see witness cones were things that I fixed early on. I added a gas gauge to measure LP pressure and fine tuned placement of kiln packs for optimal viewing.

Other more serious (and apparently common with this type of kiln) problems revealed themselves.  Getting reduction and even temperature. I followed others' advice, with a baffle shelf under the top port, and keeping bottom layer of shelves high off the floor to allow for adequate combustion. This area apparently functions like a firebox in a wood kiln, and it must be allowed to exist with this kiln, especially with the use of venturi burners. I used two analog pyrometers and quickly learned, through several firings of wide flat pieces, how loading and flow play such an important part of this kiln's functionality.  I took many notes and  conducted several different firing scenarios.  I learned how to adjust the top damper and shutter plates on the burners which gave me some insight but, results were limited at best.  Reduction was unpredictable, chokingly smoky and unreliable, even after so many changes.  I was at a loss. However,  temperature consistency inside the kiln was getting better, especially when understanding how to manipulate the top damper.

Now, this was not good enough. During several firings I was experiencing back burning. This is where the flame goes down into the burner and burns down by the orifice, rather than at the top of the burner tube. I took off the burners and cleaned off the soot. Tried again, this time with added measures (inserting screens to the burners to stop the back burning as prescribed on the clayart archives) all to no avail.  I called around for better burners (Mark Ward) but the kiln was too small for the new burners I wanted, so I was at an impass. I then looked into getting a whole new replacement burner system with a new manifold from Summit. I spoke to the owner and he told me that he, like Mark, was very familiar with these kilns. Peter Addessi told me what I needed to do, AND IT WORKED LIKE A CHARM!

Peter said that the conversion kits that he designs and builds feature venturis with no shutter plates. They fire wide open and he does not recommend the baffle shelf. So, I cleaned up the burners again, opened them wide open, and got rid of the baffle shelf. Voila! Perfection.

All in all this is no such a bad kiln after all. The design needs draft to keep the burners functioning properly. Once it is set up properly, you get very even reduction and even temperatures. I can close the top damper 2/3's closed and all peeps will reach with NO black smoke and choking unburnt fuel.

Thanks for letting me share this info. I would like to thank Peter Addessi (Summit) and Mark Ward (Ward Burner Systems) for giving me the proper info I needed to make this kiln be all that it needs to be.

Much thanks gentlemen!

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