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Mistakes I've Made with the Anagama



Firing the anagama hasn't been all kittens and cocoa. I've made numerous mistakes in each firing. You'll be miles ahead if you can learn from mine -- the amount of energy that goes into each firing is tremendous and trial by error consumes years.
collapsed shelves in anagama firing



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Collapsing shelves: This picture taken toward the end of the 6th firing tells a sad story. You can see posts and pots stuck together because the front shelf failed. But it doesn't tell the whole story -- every single shelf tipped forward into the next. The failure started in the very back row.

Background: I had been tri-posting my shelves using soaps (bricks cut in half lengthwise). Secondly, I had been making paving stones out of my scrap clay for a walkway I'm building. These tiles are about 1.5" (3.8 cm) thick and they range in width up to about 10" (25.4 cm). They're heavy. Lastly, the 6th firing was one of the hottest on record but my pyrometers did not reach the temperature level I expected. The issue with the pyrometers turned out to be related to a thick glass coating insulating the tips of the thermocouples. I got snookered by relying on the meter instead of my eye. I may have gone hotter than I needed to, but by the same token, the glaze was the best I ever had.

My Errors: First, I placed heavy tiles on the single post end of the last shelf. I pushed and wiggled it and it was completely steady. What I failed to consider was that when the kiln gets to temperature, the shelves become soft and then warp and bend. When the unsupported corner of the shelf drooped, the weight distribution changed, and it tipped forward. When it hit the shelf in front of it, it caused that one to tip forward, and the ensuing domino effect ensured that almost nothing survived the 6th firing.

Solution: In future firings, I will give up on tri-posting in favor of solid support at each of the four corners. Secondly, I will use whole bricks instead of soaps. A whole brick is much less likely to tip forward provided the narrow face points to the front and back of the kiln, and the wide face to the sides. I will lose some stacking space, but that's better than losing the entire kiln load. Last, I will think more carefully about the softness of the shelves when the kiln has been at temperature for a couple days and place pieces accordingly: heavier pieces closer to supporting posts -- lighter pieces in the middle.

failed wadding from anagama firing #1



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Stuck Wadding: Here's a lovely cup from the first firing forever stuck to its wadding. Something like this can be an interesting accident, but when half the pots suffer from such a problem it isn't even remotely "interesting". In the first firing, I had no idea how much wadding to make and not much of an idea of how to make it (this recipie isn't bad although it could benefit from alumina). I also didn't have any experience using wadding. Both issues caused problems.

My Errors: First, I didn't make enough wadding. In the end, I used plain old clay for a significant amount of the wadding work. Vitrified clay does not break off easily if it has bonded to the pottery at all. Wadding with a substantial amount of combustable components is much airier and grinds away effortlessly in seconds. I now make two 5 gallon pails full for each firing -- the extra wadding works great for sealing the door bricks. Have extra, you won't regret it.

Another point -- If you "once fire" your pottery, don't glue the wadding to the pieces with white glue. At least in my experience, the moisture from the glue tends to create a moist clay layer at the contact point between the wadding and the pot -- like a lousy slip and score job sometimes survives firing, so too do glued on wads sometimes get permanently bonded to the pottery.

In reference to the pictured wadding error, it's now painfully obvious that I should have expected glaze to run down the piece and stick to the parts of the wad that jutted out. Plus, consider the size of that wadding. What was I thinking? To prevent scars on the "public" surface, place three cones of wadding inside the foot ring. I try to set the wadding so that two of the cones face the kiln front and the third faces the back. That way a center drip has less chance of embedding itself in the wadding and doing real foot damage if it drips down that low. Additionally, if you expect the firing to produce lots of ash glaze, don't skimp on wadding height. I have numerous examples of nice pieces glazed to the shelves because they weren't raised up high enough.

Wadding mistake on foot of anagama fired pottery



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Scarred Feet: First, note the scar marked by the red arrows. I've definitely had worse problems, but even small errors can destroy a piece and necessitate long periods of dull Dremmeling. In this piece, the marked scar is at the front of the bowl, i.e., the side directly facing the fire. Glaze dripped down and bonded the wadding to the foot so securely, that a bit of the foot broke off when the wadding was removed.

My Errors: I made two mistakes which collaborated in damaging the foot on this otherwise nice bowl. First, I set the foot ring directly on the wadding. This act ensures that some of the wadding will be glazed to the piece and that the foot will break when the wadding is removed. It is better to set the wadding completely inside the foot ring thus minimizing the chance that it will stick to the piece.

Secondly, the three pieces of wadding form the points of a triangle. If that wadding triangle is arranged with a point directly under the front center of the piece, i.e., the portion most likely to collect and drip glaze all the way down to the foot, the chance that the wadding and the piece will stick together is multiplied. It is better to arrange the point of the wadding triangle so it is facing away from the fire. In this case, chances are good that drips descending to the foot will thus miss the wadding and leave behind only hidden scars on the finished piece.

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