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Firing Log

ancient kiln | 21st century logbook

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August 14, 2006

Short Anagama Firing Video

Filed under: anagama,anagama, 6th,Firing,Kiln,sound & video — odin @ 5:34 am

I video taped a little during the sixth firing, imported the tape into my laptop, and then let it languish for the last five months. I’ve been wanting to recover the 15gb of hard drive space it took up, and I was finally bored enough to stay up all night, cut it into little bits, and paste together a four minute clip.

You’ll see the anagama being fed, make a tiny steam tornado, and breathe fire. When the fire is pouring out the chimney, it’s like a river of bright water rushing over rapids. I could watch that almost endlessly.

One part may need a little explaining: about midway through the video, and at about the hottest temperature during the firing, I take out a “pull”. A “pull” is a piece specifically made to be pulled from the kiln so that the amount of glaze build-up can be evaluated. Pulls are crucial because the end of the anagama firing is determined by how well the pieces have developed ash glaze. Temperature is obviously a factor, but cones typically flatten out by the end of the first day of the three to four day wood firing period — where cones really fall down, is that they say nothing about the level of glaze build-up. By loading a few pulls, the glaze level can be checked quite thoroughly.

Without further ado, here are links to the video. Note: quicktime format; both are the same content but the 20mb clip is better quality, though a somewhat hefty download. I’d suggest doing a “save as” on the link as it might take five minutes or so even with a broadband connection.

~6mb video clip, really low quality

~20mb video clip, acceptable quality

July 26, 2006

Budget Clay Mixing

Filed under: Clay Bodies,Studio — odin @ 9:52 pm

It would be sweet to have a clay mixer and a de-airing pug mill. Of course, even setting aside the significant expense, I’d have to build a building to house the equipment and worse, upgrade the wiring at the anagama site. I have enough electricity to run some lights, a toaster oven, a tiny fridge, and a radio (I have a kick wheel). While somewhat minimal, I consider even that much a luxury compared to how things started out.

Given certain limitations on money and power, I nevertheless have a strong desire to experiment with clay. Anyone who becomes consumed by woodfire develops such urges because the claybody is a critical component of the pottery’s final appearance. For example, take two pieces, one porcelain and one stoneware, fired near each other in almost identical conditions — they will exhibit vastly divergent glaze texture, color, and coverage despite the similarity in firing conditions. For yakishime, clay experimentation takes the place of glaze testing. So how does one experiment when “necessary” equipment is out of reach?

Hint one: nothing is indispensable — alternatives always exist.

I made my clay mixer for about $75 (not including drill). Here’s the shopping list:

  • 5 gal (19 l) plastic bucket.
  • Mud Mixer (essentially a shaft with blades for mixing drywall mud — attaches to a drill).
  • Plywood and boards.
  • Plaster of Paris (yes, I bought the cheap stuff at a home store rather than the expensive stuff at an art store — it was about $10 per 25 lb (11.4 kg) sack). I used slightly less than three full sacks to make a wedging table 37x18x2.5 inches (94 x 45.7 x 6.4 cm).

Now, if you plan on making a ton of clay at a single sitting, my method won’t scale that well. But it’s a snap to make a 35-50 pound batch — although at 50 pounds, it works better to use two buckets.

Hint two: just dive in, the world won’t end if you mess it up.

First an aside. I’ve been very interested in coarse materials in my clays. One thing I’ve decided has potential is Lane Mountain Sand, a white sand sold in 100 lb (45.4 kg) sacks for about $6 at my local home store. As another aside, I’m very hip to cheap and convenient. For example, a trip to the pottery store requires either a 200 mile (322 km) round trip to Seattle, or a shorter trip to Canada coupled with a search delay on returning to the US. Apparently, the Post Office doesn’t communicate with the Border Patrol so I get tagged for using fake documents when they can’t find my “new” zip code in their database — that’s “new” as in 3 or 4 years old. Borders are stupid. Anyway, back to the digression at hand: What convinced me to use this sand in some clay is how beautifully it melts. Part of the anagama floor has no bricks — just a layer of this sand for a floor. During firing, a crust forms on the sand and in places that get a blizzard of fluxing agents, the sand melts into beautiful blue-green blobs of glass. I want some of that on my pots!

Finally, having accepted that for now, I’m looking for drippy shizenyu rather than hi iro, I mixed up this batch (do not weigh, these measurements are volumetric):

  • 2 parts Lincoln Fireclay
  • 1 part ball clay: SPG
  • 1 part Georgia Kaolin
  • 1.5 parts Lane Mountain white sand
  • 1 part Custar Feldspar (powder)

First, fill the bucket up a bit less than half full with water. Here you can see the bucket and the mud mixer I mentioned earlier:

low budget clay mixer for making stoneware enlarge

Next, add all the clay ingredients. Don’t add grog, sand, or gravel yet — just mix the clay into a nice frosting like consistency:

mixing clay the cheap way -- bucket, mud mixer, drill enlarge

After the clay is thoroughly mixed, add the sand, grog, and/or gravel bit by bit, mixing between additions and adding water if necessary. Drills aren’t as powerful as industrial mixers so the mix should be kept somewhat on the soft side — if the clay is too hard, the ingredients won’t get mixed thoroughly and it will increase the amount of wedging work. Besides, you risk burning out your drill on a stiff mix.

Once all of the ingredients are added, dump it out on the plaster wedging table and wait for it to get firm enough to wedge up. In the spirit of not following my own advice about mixing everything together wetly, I decided after I dumped out the clay that I wanted some more sand in it. Pouring sand on top of the freshly mixed clay compounded my work during wedging:

Pouring out freshly mixed clay on the wedging table enlarge

When all finished, this batch made about 35 lbs (16 kg) of clay — note the clay in the bag is 25 lbs (11.3 kg) of commercially prepared clay. The column of clay on the right is wider, deeper, and taller than the bag of clay, thus my 35 lb guesstimate:

Homemade clay all done enlarge

In terms of time: I mixed the clay around noon and then let it sit in the bucket under the hot sun all day. My purpose was to let it get warm and help incubate whatever it is that’s growing in my uber-stinky recycle clay (I tossed in a handful of recycle slip). It doesn’t hurt to let the clay mixture sit around in the bucket for a few weeks or so, particularly after adding a bit of compost starter (if you are looking for a more alive clay). Anyway, that evening, I poured the slip out on the table, added sand, and covered it with plastic (it has been hot here recently). I went home, returned the next day about mid-afternoon and it was ready to wedge. With mixing, pouring, and wedging, I probably spent about one hour making the clay … and got some free exercise to boot.

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