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Stanley IIc: "We Could Just Keep FIring, Amazing!" ~ DW
 The NCEFG's main kiln spent yet another winter underwater, even more and longer than the year before. A "crawl through" showed no obvious major damage so we decided to proceed with the season using the same kiln as in 2004 and 2005: Stanley IIb.
Stanley IIb is a single-firemouth updraught design with raised ware chamber and discrete firebox. Stanley IIb's ware chamber was made up of a solid clay interior (fired to ceramic during in the first firing of Stanley IIa in 2004) surrounded by a thick outer shell of coursed stone in a clay and straw matrix. Outside of this was a buttress of built up dirt, which tapered away from about one quarter of the way down from the rim of the ware-chamber.
 The firebox thus remained made of firebrick mortared together and covered with the same clay and stray matrix used to mortar together the rocks of the ware chamber. We also continued to use the fragments of old kiln shelves to make up the floor and lid of the ware-chamber. We kept the drilled thermocouple port on the east side of the ware chamber.
So before being put back into action in 2006, Stanley IIb's ware chamber had been fired five times and patched four times, its firebox had been fired four times, and lower underground portions had been fired eight times over four years.
For more details, diagrams and construction information please see 2004 and 2005 field notes, and Bulletins 2 and 3.
Buttressing
 We decided to build up the buttressing around our kiln all the way to rim. This would provide more consistent insulation for the ware-chamber. We hoped to diminish our internal temperature inconsistencies.
We used mostly dirt and some clay mixed with grass packed in and around fragments of old NCEFG pottery as well as whole pots, rocks, and clods of dirt.
We decided these modifications were enough to rename the kiln, Stanley IIc.
Repairs
 As in previous years we had to perform extensive patch repairs to the interior cracks of the ware chamber, which develop during the 2005 firing and propagate from a winter spent weathering. The same held true in 2006.
The mixture used to repair Stanley IIb in 2006, as in 2005, was comprised of shop clay (both white and orange clays with sand, talc, and grog tempering), mixed with equal parts fine grain river sand, and fresh grass clippings. Grass it a particularly good organic opener: it dries at the same rate as the wet clay, is less resistant to shrinkage, and is small enough to fit inside cracks in the ware chamber. Unfortunately as time goes by it also decomposes and the mixture begins to smell.
Fuel
 We decided to try using a different kind of fuel this year, in addition to our standard eucalyptus logs of the past three years.
The new wood was mostly oak, but there was also some pine and elm in the mix. These we divided into small, medium, and log (tree branch) size. The eucalyptus was, as in 2003, 2004, and 2005, well-aged, and divided into three rather arbitrary sizes: small, medium, and large.
We continued to use the weight method of tracking wood use. After cutting and sorting by size, we divided the fuel into piles of 20lbs each. This year we labeled the piles with descriptive tags, which were passed to the recorder every time a pile was delivered to the stoker's pit. This meant we were keeping track of wood amounts with both tags and field worksheets. This method proved its worth right away, as final calculations after the first firing showed the worksheet off by 20 lbs according to the tag record.
Bricks
 In 2005 we made our own bricks to replace the modern firebrick we'd resorted to in 2004.
We made them by mixing together two buckets of shop clay, one bucket of crushed kaolinite and one bucket of yellow earth clay. We formed 32 bricks by combining the above mixture around an internal body of wet straw. They were too wet to fire in 2005, but were certainly dry enough in 2006 after a year spent sitting in the studio.
Pottery
 To make the pottery we used five different wet shop clays and one field clay. All the shop clays were low fire. The field clay was from a construction site in Sacramento, California and supplied by Professor Worley.
We decided that this year one pot for each type of clay should be made to sample behavior in a more scientific manner. All these "testers" were around the same size and shape and thrown on the wheel by the same person.
The pots were constructed using the coil, slab, mold, and wheel throwing methods. This year, because of a split season, we had the luxury of allowing our pots to dry for 20 days.
Firing Stanley IIc: Brick
The day of our first firing in 2006 was slightly overcast, misty, and calm with almost no wind. These were not the most ideal firing conditions.
 Since this was a "test firing," we were not perturbed by the weather, but rose to the challenge. For this first burn we were firing the 32 bricks; several green-ware tiles with samples of glazes on them to see how they'd take a "single firing"; one huge pot, named "big-ugly," that took up most of the ware-chamber and was coated in a pink reactive lead glaze to monitor internal environment; two small pots, one of white and one of red clay, to test for ceramic temperature; and two sample objects made of our experimental field clay.
 We didn't have enough items for a full load, which would turn out to be a good thing as the weight of the bricks cracked one of the floor spars during firing. No losses, the bricks themselves shifted to become floor spars. Any more pottery and we might have had a full collapse.
As in previous years, we used the same two types of temperature measuring devices: type K thermocouples and Orton pyrometric cones. We used 5 banks of Orton pyrometric large-size cones in rows of 6 each. In order to get an idea as to how much heat was lost during transfer through the floor into the ware-chamber, we added a bank of 4 cones to the flame-chamber. We had planned on 3 sets of thermocouples with analog meters. Unfortunately our resident thermocouple expert, J. Penick, declared Thermocouple C DOA, so we had only 2. Thermocouple A we placed in our thermocouple port, and Thermocouple B was positioned to tilt down into the ware-chamber from the top edge. Unfortunately, the readings during firing were quite odd (read on).
We took the initial temperature up slowly, loosely following the graph of our most successful bisque firing back in 2004. Our preliminary stoker, I. Iasiello began the firing, with the assistance of a good number of beers (which she claimed were highly archaeological and helped alleviate the utter boredom of the first 7 hours). The oddest thing about this (and the rest of the firing) was that Thermocouple B (at the rim) constantly read HOTTER than thermocouple A (in the port and lower down) this makes no sense.
We decided that this year, unlike in previous years, we'd use smoke clues and kiln behavior to dictate firing, rather than temperature. We had no problem at all raising the temperature to about 450°C. For the first time in the NCEFG's history, we heard not a single spall. There was much complaining about the smell and smoke, which was worse than in previous years. This may be due to the amount of organic matter in the bricks, the new fuel, or both.
At this point we lost our primary stoker, and still had push to carbon immolation and ceramic temperature. Unfortunately, we stalled out at around 500?C. We pushed and pushed for over an hour eventually reaching 600?C with the use of fans. We got great gouts of black smoke as carbon burn-off occurred but we could not get flames to come up though the ware-chamber. Finally, S. Goddard jumped in and vigorously attacked the firebox, poking and rolling the coals over and forwards into the flame-chamber. In the space of 15 minutes the thermocouple shot up, flames began to appear, and we achieved ceramic temperature!
T. Borregaard, glaring worriedly into the ware-chamber, noted that glazes were vitrifying on the sample tiles and that the shoulder of "big-ugly" was beginning to bubble and over-fire. With the horror of last year's over-fired glazes still fresh in mind, she called an immediate cessation to all stoking. With only mild protests, as participants were very tired, Stanley IIc was capped and left for the night..
Results of the Brick Firing
 The brick firing took 8 hours to complete. We used 154kg (340lbs) of wood, mostly the mixed oak/pine/elm but with some eucalyptus near the end in our attempt to break 700?C. The highest temperature measured, by Thermocouple B at the rim, was 720?C. We did not melt any of the Orton cones, not even those in the flame-chamber. However, some of the cones showed stress cracking on the horizontal, which we'd never seen before and weren't sure how to interpret.
  All 32 of the bricks and both small sample pots made it through the firing. However, the two field clay samples cracked badly. While reported to take to the bonfire well the field clay apparently can't handle kiln temperatures. Also "big-ugly" cracked apart along coil lines.
Most of the glazes reached at least partial vitrification, presenting a satin finish. The inner part of "big ugly's" rim and neck did not vitrify at all, while its shoulder section bubbled and cracked. The pink reactive glaze went almost entirely white, smudging black in areas licked by flame, indicating a partial reduction atmosphere throughout the kiln.
The kiln itself did not survive the firing well. The damage was mostly to its substructure, dug into friable sandy loam, fired many times over and then exposed to 3 winter's weathering. A large chunk fell off the firebox throat where it connected to the flame-chamber.
Closer examination revealed it had fallen out from between the end of the firebox arch and the cantilevered stones that supported the ware-chamber. Worse, the wall underneath was also crumbling away. We attempted repairs, but the area was extremely friable. In the end we decided to continue with the season: at this point, the kiln was holding itself together, but it's worrying and will have to be checked after each additional firing and eventually shored or rebuilt.
Firing Stanley IIc: Bisque
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The day of our second firing in 2006 was beautiful and sunny with a brisk wind: absolutely ideal firing conditions. We had about 100 pieces of pottery, with sample tiles and loom weights all grouped together and counted as one item. This filled the kiln with 8 inches to spare. We added some pre-fired bits from last year to fill it completely and commenced firing.
Again we used the same two types of temperature measuring devices: type K thermocouples and Orton pyrometric cones.
For this firing we had three thermocouples. We placed one in our thermocouple port hole; the other two were positioned to tilt down into the ware-chamber from the rim. One of these, Thermocouple D, was rugged into our new digital monitoring laptop computer, which generated one temperature read-out every minute.
For this firing we switched back to our previous wood type: eucalyptus. We took the temperature up slowly, again trying to stick to the 2004 firing graph. During the first 400 degrees we determined flaws in both thermocouple's A and B. We fixed and replaced the necessary parts, and re-calibrated analog meters to the digital read.
We noted the usual signs of a successful firing: smoke out of the thermocouple hole, carbon deposits, and then dark smoke from the top of the ware-chamber. We were delighted to see the smoke emanating at right about 650°C, which is also the general temperature of ceramic change. We pushed the kiln onwards, seeking "the other side of black" when the carbon deposits burn away and orange flames emanate from the top of the ware-chamber. As in the past, this occurred right around 900°C. In the future, these are the signs we will use during firing.
 We continued to push Stanley IIc and reached a thermocouple reading of about 1022°C 10 hours into the firing. Amazingly the kiln did not stall, our firebox NEVER choked - it never even completely filled to top with wood. In Stanley's short life such a thing has never occurred. We could easily have pushed temperatures up to 1200°C or higher, but instead we kept it steady between 900-1020°C for 3 hours. This excellent situation may have had something to do with our stoker or our greater concern and care over lid coverage, but was probably the result of perfect weather conditions. It seems likely that if they had the choice ancient potters would have waited for the right weather before firing up their kilns, or at least scheduled firings according to what time of year produced the most favorable conditions.
At just under 12 hours in (all with the same stoker!) we capped the top of Stanley IIc to 80% and shut the kiln down for the night.
Results of the Bisque Firing
The bisque firing took 12 hours to complete. We used 186kg (about 410lbs) of wood mostly eucalyptus. The highest temperature measured, by Thermocouple C at the port, was 1022°C.
 As to our new toy: the digital thermocouple reader worked great up to about 800°C, but then malfunctioned and wouldn't read anything higher. Further experimentation seems to be necessary and our technician is on the hunt for equipment that can handle high temperatures.
We unloaded at around 2 PM, delightedly discovering an almost 100% success rate. Very few pots were damaged, none from firing except some of the Navajo Wheel clay, which warped. We have come to expect warping from this particular clay - it clearly isn't meant for higher kiln temperatures. This success rate is undoubtedly due to our extended season, with 20 days between construction and firing our pots were able to dry completely which eliminated destruction via spalling.
 The two single-fired glazed pots were slightly over-fired but quite beautiful. In the future all of our firings will be single firings, as this is more archaeologically accurate. We pronounced the entire bisque quite successful, and there was much celebration.
The kiln itself survived this firing without further substructure crumbling. The repairs made to the holes at the firebox throat seemed to have held and, thankfully, not spalled.
Firing Stanley IIc: Glaze
As always, loading the kiln for glaze took much longer than for bisque (see comments in 2005 Field Notes), about 2 hours total. We ended up having to leave several of the larger pots out. A kiln Stanley's size in the past would probably not have been producing pottery that large anyway. In the future we should confine ourselves to vessels around 6" diameter and 6" high.
We managed to fit 31 glazed pots (3 of them statues) into the kiln, using unglazed previously fired pottery as kiln furniture and saggars.
We placed 6 cone banks throughout the kiln and firebox.
The weather was worse than for the bisque firing: less windy and a lot hotter.
As always with glazes, instead of pushing our kiln to new temperature heights, we had to think in terms of reaching a specific temperature (between cone 06 and cone 04, approximately 995-1060°C) and holding it there for several hours.
Results of Glaze Firing
 Firing was short, sweet, and generally quite successful. We used only 161kg of wood (335lbs) all of it eucalyptus
The highest temperature measured by the thermocouple was 1020°C reached about 5 hours in. We suspected during firing that we may have over done it slightly either because of holding the high temperature too long or, more likely, excessive flame licking.
We had good cross-the-board cone coverage, with 08 down everywhere, and 05-04 everywhere but the very top, all without going to 02.
 The resulting glazed pots were successful with only a few of the more sensitive glazes showing bubbling. In the upper portion of the kiln two pots were under-fired, glazes labeled "transparent" or "semi-transparent" were more likely to bubble than those labeled "opaque." It's easy to see why potters of the past might select for glazes based on kiln technology. Some just work better under updraught firing conditions than others. Any glazed pot inside of a saggar did well, but was more likely to reduce in color. So were those closer to the bottom. No glazes melted off. The range in temperature and atmospheric condition inside the kiln meant that a glaze could result in a wide spectrum of coloration.
All NCEFG participants went home happily clutching at least one beautiful pot.
tarray of cracks, but no major damage. Consequently we shut Stanley IIb down for yet another season, left to weather the winter months once more.
The End of the Fourth Year
 2006 was a successful season. Despite structural flaws, new stokers, and the new "visual clues" approach to firing, Stanley IIc performed remarkably well. Our bisque firing techniques in particular are getting better.
In our quest to replicate ancient methodology we used smoke clues, rather than thermocouples, to decide when to stop firing, though we kept the thermocouples in place for scientific reasons. Also we showed that single firing with modern clays and modern glazes was a viable option. In the future all our firings will be single glaze firings. We must continue to keep a close eye on those pots that can be seen in the ware-chamber and use as many saggars as possible.
We'll attempt to keep the extended season. Our fantastic bisque survival rate was clearly due to the fact that the pottery had 20 days to dry between manufacture and firing. We MUST continue this practice, especially in conjunction with single-glaze firings.
For more scientific conclusions and analysis, as well as additional details, please see the 2006 Field Report in the Bulletin of the Northern California Experimental Firing Group Vol. 4 (currently in production). |
