Last Friday afternoon, I stopped by my friend’s office and picked up a chunk of his property — neatly contained in a ziplock bag. Then on Saturday, I pounded up the block by wrapping it in a heavy plastic bag and sieving out the powder.

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Once I had a bowl of dust, I took it into the studio and made four test clays (all measures volumetric, not weight based):

1. 100% test clay. Back right in photo below.
2. One part test clay, one part Helmar kaolin. Back left in photo below.
3. One part test clay, two parts Helmar kaolin . Front right in photo below.
4. One part test, one part Helmar, 2/3 part silica, 2/3 part Custar feldspar. Front left in photo below.

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I poured each test out like a pancake on the wedging table with Silver watching and perhaps wondering if they were tasty cakes for cats. After a few hours, I was able to wedge the clay into four little balls. From these, I quickly whipped up eight pinch pots and marked the bottom of each piece with the number corresponding to the test clay. Each of the clays was pretty short and edges tended to break and separate.

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Sunday came like Christmas morning — a burning day — and I returned to the kiln great anticipation. Unfortunately, Saturday night was comparatively cool and the pieces had not dried — they were at the perfect leather hard trimming stage. I decided to fire them anyway. Besides, what better to fire wet pottery than a wet kiln?

I haven’t used the raku kiln in a long time and so when I pulled the tarp off the base bricks, they had all turned green with mold. Additionally, an entire colony of snails was living quite cozily in the moist damp undersides of the tarp. As an aside, I wonder if this has been the source of the large snail population this year. I find it disturbing to walk around in the grassy area behind the studio — it seems that every fourth or fifth step results in the sickening pop-crunch of a snail being smushed.

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After rescuing as many snails as I could find by putting them out in the tall grass areas in which I don’t walk, I set about loading the raku kiln. Because the pieces were substantially wet, I placed the shelf high above the burner port to reduce the risk of explosion. Then I candled the kiln at the lowest reliable flame, gradually increasing the temperature until the pieces appeared dry when I peered into the kiln. Once I got to that point, the fun began. I removed the regulator from the propane hose so I could a big jet of flame, and gradually began raising the temperature. Once I hit red heat, I let it roar. When that burner is tapping propane straight from the tank, it sounds like a jet engine.

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I knew I couldn’t get to cone 10 with the raku kiln, but during the firing I began to wonder how high I could go. I grabbed a spare unused pyrometer I had laying around and inserted the probe between the brick base and the fiber kiln body. Toward the end of the firing, I stoked a medium sized log into the kiln — chopped up into kindling of course — stoking two small sticks at a time. Eventually, I was able to get to 2200 F and held it there for a short time (given enough time, this would equate to about cone 5 when firing quickly). It was a hot day and the wood chopping, such as it was, made it seem hotter. I figured that was good enough for a test and called the firing.

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I was intending to open the kiln raku style right then, but I suddenly realized I was wearing shorts and had brought no pants, so I just closed up the kiln and decided to wait till it reached a temperature that wouldn’t blister my legs. Eventually, the temperature dropped and I was met with an amusing sight — a lovely puddle of glaze where the “pure” dug-up clay cup had been:

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Results:

#1: 100% dug-up clay. I love this glaze with the subtle variations of black and brown. A hot mud spring frozen while burbling — or a really flat cup (below):

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#2: 1:1 | dug-up:Helmar. This piece is slightly self-glazed (below):

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#3: 1:2 | dug-up:Helmar. This piece is quite dry (below):

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#4: 1:1:2/3:2/3 | dug-up:Helmar:silica:custar feldspar (below):

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#4 is rather interesting. It is self-glazing and incredibly porous — I know this because I broke it a little prying it off the shelf and the clay body is full of pinhead size holes (you can see the scar on the rim in the picture above). Perhaps it would make interesting insulating mugs. The porosity makes it feel extremely light though — so light that it feels “wrong” somehow.

Fred Herbst is a ceramics professor at Corning Community College in upstate New York. Interestingly, google satellite data for Corning is quite good although the kiln had not yet been built in this shot: aerial view of Fred’s anagama site. Check out Fred’s online gallery for a closer view.

Fred Herbst and daughter Emma.

During our discussion, we spoke about Fred’s anagama and one of the more unusual ways in which an anagama may be used: as a furnace for glass blowing. We then move into his experiences with reduction cooling experiments and how this technique benefits iron rich stonewares, but how a more oxidizing atmosphere tends to favor porcelain and white stoneware.

In the photo gallery accompanying this podcast, you will find pictures of Fred’s kiln, its construction, firing, and examples of the finished work. Fred has also graciously provided a set of clay and glaze recipes. Pay particular note to Fred’s Porcelaineous which fires beautifully — much like a Shigaraki clay.

If you wish to fire with Fred, you’re in luck. He is hosting a summer workshop, July 10-16, 2007, with Jody Johnstone. The cost is $200 and if you are interested, contact Fred (email below). If you can’t make the firing but find you are interested in having a piece fired in Fred’s anagama, contact him directly: herbstNO@JUNKcorning-cc.edu (remove “NO” and “JUNK” for correct email).

Last, some links related to topics brought up in our discussion:

• Dick Lehman’s article: A New Approach to Long-fire Results.
• Fred’s kiln was designed by Simon Levin.
• Some history about Roman Glass, the type of glass that was recreated in the anagama glass blowing experiment.

Image courtesy of Arthur Rosser.

Steve Harrison is a potter from Australia with decades of woodfire experience under his belt, plus an obvious love and ability for the geological sciences as applied to ceramics. To understand the breadth of his experience, take a peek at his CV, or consider that he is currently firing work in a kiln he built himself out of bricks that he made from local materials; the pottery fired in the kiln is made of clay he collects locally, glazed with materials he collects locally, and fired with wood grown locally.

photo gallery of Steve Harrison’s work, bricks, and kilns. Photo courtesy Michael Bradfield.

His work is shown (and available for sale) at the Legge Gallery in Sydney Australia. During the course of the podcast, Steve discusses his current show “Dirty Little Secrets” and how he developed the clay body used to create these examples of black-bodied ware (as well the white porcelain work represented in a prior show “From the Ground Up“). His recent work is influenced by the way “perfection” has been devalued by modern manufacturing techniques. You can read more in an article he wrote entitled: Perfect Is the New Junk (pdf, © Steve Harrison, used here with permission).

Steve’s kiln building/rock glaze books are available directly from him. Additional photos of his studio, kilns, and work can be seen on his Sidestoke page. Lastly after talking with Steve, I had much to google. Here are some of the more interesting things I picked up:

• Steve has an article in Ceramic Review, Issue #222, entitled: From the Ground Up.
• Porcelain Spy: Père d’Entrecolles. Read translations of his actual letters or a summary written by the NBH (Hungarian Spies) entitled: Pioneers of Industrial Espionage. (as an aside, the entire NBH site is rather interesting, even if a bit chilling).
• Porcelain requires Baitunze (also spelled petuntse, petunse, baidunzi, and likely more).
• Picture of “treacherous” bauxite pebbles (scroll down for a picture of a hand full of them).

I think you will find that Steve’s interview, aside from being interesting and entertaining (Steve has a great sense of humor), will foment a storm of ideas. Enjoy.

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 37×18x2.5 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:

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

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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:

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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:

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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.

Musings aside, before the last anagama firing I mixed up a batch of “clay” which I had hoped would develop colorful hi-rio (I say “clay” in quotes because it had very little actual clay in it). I must have been drunk or distracted because what I made was something destined to be glassy — and I knew that as I was dumping everything together — I just didn’t really think about it. Secondly, I did a two hour period of quick cooling at the end of the firing in which I used this clay. Quick cooling an anagama brings out the gloss and wipes out orange and red. As I mentioned — my actions say I want glassy shizenyu, not hi-iro.

CORRECTION — I mixed up my measurements here and after making this clay the other day, I wondered why it was so darn short and unthrowable compared to the first batch — looking back at my notes, I see halved the clay measurement and doubled the feldspar. That should make an interesting test!

Here’s the recipe. Take note however, all measures are volumetric — no scales were harmed in the making of this “clay”:

• 40% 20% Custar Feldspar, crushed 10 mesh (not powder)
• 40% silica
• 20% 40% Lincoln Fireclay

As one might expect with all that glass making stuff, I didn’t get bright orange fire-color. Regardless, this clay is yummy. The anagama gave me a shizenyu piece that ranges from steel-blue to aquamarine. The glaze surface is exceptionally deep and three-dimensional. Some of the feldspar granules were too tough to melt and the white speckles give it a coarsely polished-rock sensibility — sometimes sharp, sometimes smooth. I love its obsidian rock-like qualities.

On the downside, throwing this clay is like throwing knives — not in the circus sense of course, but imagine a clay body full tiny blades. That’s what this one is like. If you make it, I suggest you sacrifice some sponges instead of your fingers.

Enough chatter though, pictures are worth more. Do note, the chunk taken out of the rim is my fault. In my exhaustion at the end of loading the kiln, I grabbed this jar roughly:

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Color in protected areas isn’t bad:
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Oily streams over clear glaze. In person, this glaze is deep — it’s possible to see under the streams which float over clear layers:
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The sort of fuzzy white looking stuff on the foot is bonded but unmelted sand. I didn’t wad this piece — I just set it on the floor sand. But what a nice blob of multi-dimensional glass in the center this shot:
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The following pictures show something very interesting about this clay. First, this piece is simply a small cup. In the shelf failure that ensued in the 6th firing, it was pushed up against something at the place you see the blobby brown scar. When it was detached, a chunk of the piece was pulled away below the brown patch.

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Here is a detail of that area. Note the peach colored network surrounded by cells of white body — that peach colored material is the fireclay. Everything else is glass from the silica and feldspar. This “clay” is mostly glass with some fireclay glue to make it stick together and hold its shape.

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I’m curious about what this clay would do in a regular gas firing. If you should conduct such an experiment, please send me a picture.

First, let me describe more fully what I want. Furutani fired pieces with incredible firecolor. I have wanted the same result for a long time, but the closest I ever came was orange wadding. I have brown and blue coming out my ears, but no reds.

I can’t speak for all anagamas, but in my firings of unglazed pottery, color is most directly related to clay. Porcelain is generally white. B-mix is sea green on the front, and rust colored on the back (I don’t like the rust). Clays from Seattle Pottery Supply are varying degrees of brown (Sea Mix (brown/tan), Delta White Stoneware (dark tan), Sclupture Buff (very dark brown). Never a red.

At one point in time, I was trying to concoct clay mixtures that mirrored the chemical composition of Shigaraki clays. There were some interesting results, but never a red. I feel my failures were related to the fact that clay is a suspension of particles rather a mass of disolved elements. Think of it this way: let’s say I’m trying to make a clay that has a chemical composition of 1a, 2b, 3c, and 4d (numbers indicate amount of mineral, letters refer to different minerals). Potters make the original clay out of two rocks, rock-one’s chemical analysis is 1a and 2b; rock-two’s is 3c and 4d.

I have at my disposal different materials: rock-a’s chemical analysis is 1a, 2b, and 1c. The other is 2c and 2d. Then I add some pure “d”, two units, and end up with the same chemical composition as the original, but a completely different clay.

You should have seen the spreadsheet — it was pretty nifty. But all that nift didn’t give me firecolor. So, back to the wadding. For whatever reason, the fireclay/silica/grog/rice-bran mix often turns bright orange. Two nights before loading day I suddenly decided to make a wadding like clay. It was two parts Lincoln Fireclay, two parts silica, and one part 10 mesh custer feldspar.

I think it was a good idea to finally give this a shot. But I made a mistake in my haste and exhaustion.

Firecolor does not come about on pieces with lots of ash glaze. Feldspar granules tend to melt and make a glassy smooth glaze. What this means is that my recipe will work against itself. The high silica content should resist glaze formation while the grains of feldspar will be slobbering glaze all over. I suppose it could be interesting, and we shall see, but I’ll have to make another go at the wadding-like clay for the next firing — one that doesn’t work against itself.

• 2 parts silica
• 2 parts grog
• 3 parts fireclay
• 5 parts rice bran
• Zero parts mouse droppings

I bought a new sack of rice bran today. I like to use bran for my wadding because 1) I can get it, and 2) it works great. It’s important to have a reliable source for any raw materials you use. Apparently, rice bran is fed to horses to give them a shiny coat which means I can get it for $16.99 at a local feed store. I wish they had a $10.99 sack though. At 50 pounds, I don’t really know what to do with it all.

The last time I bought rice bran, I stored the leftovers (most of the sack to be precise) for the next firing. The next firing rolled around and what should I find — a sack of moldy bran dotted with black beads of mouse stuff. I sighed, did my ineffectual best to separate the little gifts as well as I could, and mixed up my wadding. The nice thing about this fresh sack of bran: no mouse dirt. I think I’ll just give the bran leftovers to the neighbors this time — they have horses — and I’m not too keen on mixing up a batch “ick” wadding next fall.

My clay mixer is rather simple. I have two plastic five gallon buckets, a mud mixer (for plaster — look in the sheetrock section of a home store), and a drill. I put some water in a bucket, some clay, mix with the mixer attached to the drill and make a moderately thick slip. Then I simply keep adding materials and water till I have enough. I mix the silica, clay, and grog first. Once that is mixed, I add the bran and give it all a final mixing.

I need to get a corded drill though — I went through three batteries today and still had to resort to using a stick to finish the job. Not easy because once the bran goes in, the stuff has the consistency of old thick oatmeal with a dash of concrete. It smells pretty good though — bready.

Once I’ve mixed it up, I dump it out on a plaster table, crank up the heat, and wait for it dry out enough to wedge up. As it gets dry, it gets pretty crumbly so it is important to keep it from drying out too much. It must be moist enough to press into little cones (or big ones depending on the size of the piece it will support). Be aware that the wadding will dry much more quickly than plain old clay when using the wedging table method of clay making.

The rice bran gives it a very odd feel. Even when wet, you can handle it and make it do basic things. Clay without the bran at that consistency would be slightly less workable than room temperature Crisco. With the bran in, it behaves very differently. I’ve been thinking I might try making a small kiln using the wadding as a roof. I also think the wadding itself has the potential to be used in making pots. Surprisingly, some of the best fire-color to come out of the kiln has been on the wadding, not the pieces. You want to know frustration? That’s frustration.

Hmmm … I hope the mouse dung had no responsibility for the great oranges and reds in the previous batch of wadding.

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1. Wadding is nothing more than lumps of clay placed between the pieces and the kiln shelves. Salt fired and wood fired kilns require wadding to elevate the pieces off the shelves. If the pieces are placed directly on the shelves, they will be forever bonded to the shelves by the atmosphere induced glaze. I use rice bran in my wadding because it burns out. That way when a piece of wadding sticks to a pot, it breaks away fairly easily. Solid clay doesn’t work so well. I knocked the feet of at least half my pieces in the first firing because of lousy wadding.