Monday, February 13, 2012

Natural ash on Decorated Pots

Ash buildup works nicely here

Several pieces from my latest wood firing are pots that have been decorated by carving designs through a dark slip on a light clay body. It's sometimes difficult to know how to place them in the kiln.

Do I want to take a chance of having the design obliterated with ash buildup? Do I place the pieces so that most of the design work is hidden from ash?

When I decided to build a wood fired kiln, I decided I wanted a kiln that would help create a lot of ash buildup and flashing. I want people to see the pot and know it's been wood fired. When carving on a piece for the wood fired kiln, I sometimes carve on just one side of the piece, and place it in the kiln with the decoration to the back, or to the side, so that ash build up doesn't obliterate the design.

But sometimes, ash buildup around the design happens in such a way as to enhance the design. I have been carving a lot of trees on pots lately, and a few have lovely additions of ash around the limbs of the tree that look like leaves on the tree. I placed a few pieces this firing so that the design faced forward. And some of the pieces I carved had a design around the whole pot, so that I couldn't hide the design from the ash.

Here's a few pictures of pots with design work from the latest firing, showing first the "front" of the pot, then the "back" of the pot. We did stir the embers and the firebox a lot during the firing to create more ash buildup, as well as use a technique of raising and lowering the temperature between 2,300 degrees F. to 2,100 for a couple of hours. And we threw in a few handfuls of ash and sawdust toward the end of the firing.

More pictures from the firing can be found on my Facebook page, here.

 Ohio clay slip

 South Carolina clay slip

 Ohio clay slip

 Ohio clay slip

 South Carolina clay slip

 Ohio clay slip

 South Carolina clay slip

Thursday, February 9, 2012

Going for more Ash Buildup

What a great firing we had yesterday. I started feeding the kiln small sticks of wood at 5 a.m. We finished up at around 7:30 p.m. That's a 14 1/2-hour firing. We employed a technique we read about in Japenese Wood-Fired Ceramics. Utilizing the pyrometer (high-fire thermometer), we brought the kiln from 2,300 degrees F. down to 2,100 and back up to 2,300 repeatedly for a couple of hours or more. This is supposed to create more buildup of ash on the pots. We also threw in a few handfuls of sawdust mixed with some ash collected in the bottom of the kiln's chimney.

We reached a temperature of around 2,500 degrees in the very front of the kiln. The picture at right shows the last pyrometric cone (cone 14) bent at the end of the firing. Cones are made to bend at specific temperatures and are the most accurate way of measuring the effect of time and temperature in a kiln.

The bowl on the right is glazed in a shino glaze, which received a lot of ash. You can see the ash as texture on the pot. The other pot is a tea bowl by fellow potter Phillip Pollet.

Cone 14 is quite hot. I'm not sure how accurate a reading you get when reading cones in the front of a wood kiln. They are blasted with ash and other volatilized compounds, which might affect their performance. Same goes for the pyrometer at this degree of heat. The digital display of temperature begins to fluctuate more than usual. If I can remember to do it, I'm going to set some cones in the front of the kiln next time behind a shelf post to protect it from the ash and see if it makes a difference.

We're pretty sure we reached cone 10 (2,340) toward the back of the kiln, and we're hoping for cone 8 or 9 in the very back (we neglected to place a set of cones in the very back where we could see them).

Here's a few more pictures:

 Pots on the floor of the kiln next to firebox

 A glazed bottle at the back of the kiln 

 Posing potters Levi and Michael...
Firebox door was left ajar, and a 
brick was pulled out.

Toward the end of the firing

Thursday, February 2, 2012

Getting Started on Firing #22

It's been nearly three months since we've fired the wood-fired kiln, our beloved Manabigama, as it's called by its designers. So, Levi and I took advantage of a lovely warm winter day today and started loading for firing number 22 (I think).

We enjoyed the lazy weather and weren't in any rush to get it done, as we're not sure when we'll fire - probably next week. We loaded four of Levi's tall vases.

We decided to set a couple of Levi's narrower pieces on a small piece of kiln shelf brushed with kiln wash and dusted with sand. We thought wads on the bottom wouldn't be stable enough. Wads made of sand, sawdust and clay are usually placed between the bottom of pots and the shelves to protect the pots from sticking to the shelf when ash from the wood gathers on pots (and under pots) and melts.

We put Levi's tall vases in the back of the kiln, where the kiln is cooler and ash doesn't melt as much as the rest of the kiln. So, we shouldn't have trouble with ash melting around the bottom of the tall vases.

We'll finish loading tomorrow, and then it's off to the spaghetti dinner in Asheboro for the Uwharrie Mountain Run participants. I'll be delivering all those awards we've been working on for the past three months. I can't wait to be stoking again.

This is as far as we got loading the
kiln. We used two full shelves in
the middle of the kiln so we could
place a large tree platter on one.

I've fired only three large platters
in this kiln, and each one warped
or cracked. This one is a bit smaller
in diameter, so maybe it will survive.

Levi's tall vases. The two in the middle
are glazed in a blue glaze for a customer.