The Leupp Kiln Conference began in 2003 when Tim Wilcox, a Navajo/Tewa archaeologist, artist and potter, volunteered to host the event at Old Leupp (near Winslow, Arizona). This very informal gathering of archaeologists, potters, replicators and other interested folks has been held almost every year since at various locations in the American Southwest, depending on who volunteers to host the affair. In addition to firing various pieces of pottery using a whole range of firing methods and fuels (incuding trench, pit and surface kilns), one day of the two or three day event is dedicated to visiting clay sources in the local area to collect clays to make pots for future firings. A major purpose of the event is to explore the techniques and technology involved in non-modern ceramic firing, but getting together with like-minded folks to burn a lot of wood, coal, animal dung and even corn cobs and to learn from each other is just as important.
The 2012 Leupp Kiln Conference will be held at the Tarnoff Art Center in Rowe, New Mexico. The entry fee for participants is $25 and includes bar-b-que on Saturday evening and entry into all events June 22-24, 2012. For more information click on http://www.potteryoftheancients.com
The following slide show presents selected photos culled from the archives of past conferences. After that is the final report of the 2011 conference.
2011 Leupp Kiln Conference Report
William A. Lucius, Bob Casias and JoAnn Weldon
The 2011 Leupp Kiln Conference was organized and hosted by Bob Casias and JoAnn Weldon and held at Pecos National Historic Park, New Mexico, contingent on the lifting of a fire ban due to persistent drought conditions. Originally scheduled for late July, the event had to be rescheduled to Labor Day weekend, September 2-4. Participants arrived beginning Friday afternoon to begin preparations, followed by demonstrations on the Visitor Center Portico on Saturday morning for the benefit of conference participants and park visitors. Steve Rospopo demonstrated micaceous clay building techniques, followed by a demonstration of mug building using carbonaceous clay by Bob Casias. JoAnn Weldon presented polishing and painting techniques and Bob Casias finished up with polishing and painting with beeweed (organic) and manganese (mineral) paints with Yucca brushes.
Preparations and firings were scheduled to begin in the afternoon in the Adobe-Making Area, but an intense rain storm of some duration forced us under shelter and effectively extinguished preheating fires that had been started. However, after the storm abated preheating fires were reset at the various kilns. In all, five different kilns were fired by four different kiln bosses, assisted by various kiln conference participants. The following kiln reports were submitted by the kiln bosses as a summary statement of their firings. Thank you to the various participants who provided copies of their photos for illustration of this report.
Bob Casias - Reduction (Black-on-white) Trench Kiln Firing
The day that began with ominous, overhanging clouds and rather damp conditions overall due to the welcomed return of monsoon moisture. As my good friend Clint Swink, once said, “The Anasazi didn’t fire on rainy days; they didn’t have to worry about weekends and weekday scheduling.” But here we were again pushing the envelope on firing conditions. The preliminary firing was ignited around 10:00 am with the expectation of loading the kiln and igniting the secondary fire by noon. However, a major downpour forced a two hour delay - the base fire I had started had turned into damp, fine ash. Additional fuel was added to ensure a good bed of coals were in place. This primary fuel is important as its re-ignition allows for greater temperature rise during the second firing phase. Pots were placed around the exterior of the kiln to warm them and bricks that belonged to the Park were used to keep the dry pots off of the wet soil.
Most of the pots were of similar height but Bill Lucius brought several larger bowls and a large jar that required more depth to accommodate these larger pieces. Once the second round of primary fuel had been again reduced to chunky charcoal, the kiln furniture was placed in the kiln, making sure that adequate air flow existed to bring ventilation to all areas of the setting. The pottery was loaded into the kiln and cover sherds were placed above the top of the unfired pots. Because of the difference in height of the pottery being fired, some areas of the kiln interior were exposed to more draft, while other areas remained less ventilated. Later photos will demonstrate the difference in firing results because of this. Large spanners were placed across the top of the kiln and then pieces of juniper were placed as rafters in order to keep the secondary fuels suspended above the setting for as long as possible. Although the firing began with normal wind speeds, within twenty minutes of ignition the wind had picked up dramatically and forced oxygen into the kiln’s atmosphere raising the temperature quickly. It was during this high wind we heard several loud explosions, which signaled the large jar and bowl had cracked and split apart. The intensity of the wind had wind caused the temperatures to rise dramatically. Because of a faulty pyrometer, we were unsure of the temperature at this stage of firing. The firing progressed for about an hour and a half until most of the secondary fuel had been exhausted. The kiln was buried using the soil saved from excavating the pit. We left the pottery to cool overnight. It rained again heavily overnight but the mounding of the soil allowed the water to run off of the kiln without infiltrating the interior.
The next morning we carefully removed the cover soil and were pleased to see that the kiln firing had reduced the iron in the clay body and the beeweed had done its magic, producing a nice black image on a brilliant, white background. There were no pots that appeared to be overly oxidized and the slip clay was indeed very white! A testimony to the versatility of the Mancos grey clay that I use is that none of those pieces made from the Industrial Park source cracked. There was some warping of one bowl and a handle of a mug that exploded due to a trapped air pocket, but the most pieces survived. The Cannonball White Source slip clay was good with only one or two pieces looking smoky and cloudy.
One of my bowls (the dual bat design) was in a part of the kiln that never cleared the carbon on its surface from gases produced from the burning wood and this bowl came out looking very dark and murky. I later re-fired this bowl in a better firing environment and cleared up this free carbon. I have included that photo of before and after to demonstrate that ideal conditions can produce better results.
JoAnn Weldon - Non-traditional Black-on-black Firing
When the rain settled down to a light drizzle, we inspected the coals we had started for a surface oxidation kiln and found them still quite hot, so we decided to use them for an alternate non-traditional black on black firing. A flat heavy metal plate was placed on top of the coals, dry sand was spread about an inch deep in a circle around the center of the plate, sandstone slabs were placed in the central area, hardwood shavings were placed in and around the sandstone and the pots and shavings covered with the metal container, being sure to push the container down into the sand to seal the air out. Immediately a log cabin fire was built around and over the metal container and set afire. Three different types of pots were selected for this firing, a micaceous pot, a small, corrugated pot, and a highly polished and painted cut-neck pot. Only the cut-neck pot obtained the desired black on black finish.
JoAnn Weldon - Oxidation Firing
In preparation for the above ground oxidation firing, another shallow pit for the coals was dug and loaded with wood, which was allowed to burn down to coals. The pots were set around the outside of it and rotated occasionally to preheat them. When the coals were ready, metal grates were place on the coals to form a level base. Sandstone slabs were place on the grates and the pots positioned on them. A cribbing of wood was placed around and over the kiln. The cribbing was set afire from the top and the top was burning well when the wind started to blow very hard. Because the wind seemed to be cooling the kiln, and an attempt was made to block the windward side with more fuel to cut down on the draft. This helped, but the color of some of the clays indicated that the kiln never reached good firing temperature. Because we had to leave by 6:00 pm, a small amount of still burning fuel had to be removed and quenched. At this point, some of the pots in the kiln were clearly exposed, but appeared to be intact. Mother Nature decided to add insult to injury, and it started to rain again. The larger exposed pots had not cooled down enough to withstand the thermal shock caused by the rain. Many of the smaller pots, especially those made of red clay with high temper content survived. The next morning the exposure and breakage was evident.
This oxidation firing must be considered unsuccessful or marginal at best. Several factors contributed to this. The pots were spaced too far apart. Because of the spacing, there was not enough cover sherds to help shield the hot pots from the unexpected rain. The kiln should not have been lit from the top. In the strong wind, the heat from the top logs was lost before the sides ignited properly, resulting in a marginal firing temperature. Inspection of two larger vessels that broke or cracked, show a pattern of cracking that originated at a point that was on top and exposed when the rain started. Generally, the red ware pieces fired reasonable well, but buff and white clay pieces did not reach adequate temperature, based on the final color. Color variation on two red slipped pots indicated that the temperature around these pots was more uneven than usual, and this was probably true throughout the entire kiln. A smaller kiln and smaller diameter logs for the cribbing might have helped reduce the cooling when the wind started to blow. The final lesson learned can be stated in one sentence – “Don’t let rain fall on your hot, exposed pots!”
Surface Micaceous Firing - Steve Rospopo - No report available
A Manual for Replicating Pueblo I, Orange Ware Pottery - William A. Lucius
Introduction
At the suggestion of Rod Swenson, a first-time attendee of the Leupp Kiln Conference, I converted my kiln firing report into a manual for those interested in making and firing oxidized pots. The following photos are from the 2011 firings. It should be noted that orange pottery refers to a very specific tradition that requires access to clays available only from the very uppermost portion of the Morrison Formation. Not surprisingly, prehistoric orange pottery is associated with the Blanding, Utah area – the epicenter of red clay availability. The prehistoric pottery types Abajo Red-on-orange and Bluff Black-on-orange were made only during the Pueblo I period, from approximately 750 to 900 A.D. Even though any potter would class it as oxidized earthenware, it is very different than the soft, sandy, riverine clay bodies used by the Hohokam, Iroquois, Egyptian or Danubian potters. The red clay beds appear to be reworked smectites (derived from volcanic ash) that were redeposited with iron oxide and quartz sand. As such those clays are somewhat silty, non-swelling and quite dense. Iron acts as a strong fluxing agent and therefore those clays are not suitable for reduction firing. Oxidation firing at temperatures below 950 degrees C minimizes the possibility of bloating and vitrification. The iron content results in surface colors in various shades of orange. I know of no commercial clays that might substitute for these native clays.
The general Blanding locale also contains manganese dioxide, iron oxide, limonite and white clays, all of which may be used to make various mineral paints. Commercial, ceramic grade versions may be substituted. Beeweed occasionally can be collected in association with fields in Montezuma Creek, and when boiled down to syrup is a necessary flowing agent that must be added to the mineral constituents. Additionally, narrow leaf yucca, which is what I use to make paintbrushes, is common in drier areas around Blanding.
Finding the Clays
In general, the red clay outcrops appear where erosion has cut through an overlying sandstone cap that extends from the Abajo Mountains south to the San Juan River. However, only a small number of those outcrops contain clays with sufficient plasticity for pottery manufacture. In general, those clay outcrops form an arc from Alkali Ridge on the east, across to Blanding, which is on White Mesa west to Big Canyon and as far as Brushy Basin. If you are interested in gathering any of these clays, please feel free to contact me for specfic location data in the form of GPS Coordinates. Be forwarned that several of the sources are best approach in a pickup or high clearance vehicle.
Processing the Clays
I use large, 30 gallon plastic trash cans, one of which I fill half-way up with water and then slowly pour in dry clay chunks. After letting it soak I mix it using an electric drill with a hefty paint mixer attachment to achieve a thin, watery consistency, which allows the heavier fraction to settle out. I then transfer the clay soup into another 30 gallon trash can, pouring it through galvanized window screen tacked onto a wooden frame for ease of use. This step is critical because the weathered clay always contains a fair amount of juniper berries and twigs, roots and other organics such as rabbit pellets. Discard what gets caught in the screen and clean the trash can, so that you can return the clay to the original trash can, using the screen to catch any missed bits. Cover it and in a day or two you can begin to pour off the clear water. Over a period of time (less if you can let the clay freeze and then thaw) you can remove a substantial fraction of the water. A plaster bat allows you to quickly dry the clay out to a workable consistency.
Or, if you want, just make a mound of the dry clay with a depression in the middle and add water much the same as you would make pasta dough, adding small amounts of water and mixing until you achieve a soft clay body - it should slake down easily. Of course you do not want rocks or juniper berries in you clay so you might have to pick them out by hand.
Adding Temper and Kneading
You must add a tempering agent to the clay body. Temper serves to “open up” the clay body and reduce heat shock that is inherent in pit firing. The best option is to use diorite, an igneous river cobble widely available in the Blanding area. The best way to break it down is by repeatedly heating and cooling it in a campfire until the rock crumbles into small pieces. A mano and metate (or a hammer mill if you happen to have one) can be used to finish processing the temper. Grog (ground up sherds) also works well. Quartz sand of any type is likely to result in firing cracks and should be avoided. The coarser the temper, the less likely it is that the pot will explode. The amount of temper should be at least 30% by volume, but really you need to experiment to determine how much to put in. Remember that adding temper decreases the plasticity and if the clay is too gritty you should reduce the amount of temper by adding more raw clay.
Make sure to knead the clay thoroughly after adding temper to make sure that everything is evenly distributed. Kneading also forces clay, temper and moisture together, and in doing so initiates the aging process, which allows the remaining organics in the clay to rot, which increases plasticity. The longer you age the clay the easier it is to work with. Wrap it tightly in several layers of plastic (plastic shopping bags work well) and put it away in a damp place for up to six months. But if you cannot wait, just start making pots immediately.
Forming the Pot
I prefer to throw my pots on the wheel, but if that is not an option you may hand build them, using a puki or an open bowl as a rotating base. Unlike later pots, X-rays document that orange ware pots were made using flat fillets, or fairly large coils that were flattened to approximately the desired vessel wall thickness and stacked end-to-end and on top of each other and then scraped to smooth the joins. I would suggest that you start out with a circular pad of clay at the bottom and then begin building the pot on it, which in prehistory were overwhelmingly bowls. If fillets do not work for you, you can construct the bowl by using a continuous coil (approximately the size of a Number 2 pencil). Pinching the coils down over the preceding coil creates a clapboard effect, which results in strong, even walls. Use a gourd or wood scraper to obliterate the coil junctures. Handles on orange ware pottery are rare, probably because they tend to pop off easily. Also, vessel walls must be of consistent thickness; any variation tends to result in cracks. Avoid thick bases.
When done, set the bowl aside until it stiffens enough to be handled without deforming. Be careful to keep it away from drafts or direct sunlight, which leads to unequal drying stresses. At that point tune up any imperfections and use your hands and water to smooth the surfaces for polishing and painting.
Polishing the Pot
Polishing involves using a smooth stone (dinosaur gastroliths work great!) to compact the surface of the body clay. Pick your stone carefully as it needs to be hard enough to develop a mirror polish from use. Prehistoric potters were often buried with their polishing stones for use in the afterlife! If polishing is initiated too soon the stone will pluck out bits of clay and if the pot is too dry it will only hit the peaks and leave the valleys dull. Polishing effectively decreases the porosity of the clay and results in a smooth surface suitable for painting. Orange ware pots never appear highly polished, perhaps in part because a mirror polish interferes with paint adhesion – the paints just rub off after firing. I usually polish the bowl overall when still damp and then rub the polish down with a soft rag, which effectively mutes the shine.
Making and Applying a Slip
Slips are nothing more than clay slurry which is added to the surface of the clay body to change the surface color. And like gesso it provides a smooth surface for painting. Begin by adding a small amount of clay to a large amount of water. Agitate with a paint mixer until the clay is totally dissolved in the water. Pour the clay water through the finest nylon screening material you have (nylon stockings if you have access to them) to remove any organics and then pour it back into the original bucket. Let the mix set for approximately 5 minutes and then pour the mix into the second bucket, making sure not to include the coarse (darker) fraction in the bottom of the bucket. Discard that, agitate again and repeat the process, discarding the coarse fraction until none appears in the bucket. At that point cover the bucket and let it sit a day or two until you can pour off the clear water. Continue draining off the water until you obtain a creamy consistency that lightly coats your fingers when you dip your hands into the bucket.
If you wish to turn your pot into a redware you will need to add a small amount of powdered iron oxide (you will have to experiment with percentages) to your orange clay. Knowing when to slip comes with practice. Apply the slip when the bowl or jar is still damp. The Blanding red clays do not usually crack when dipped or brushed with a slip. If you let the vessel dry too much the slip will probably craze and perhaps even fall off the body clay. If you need to put a handle on your pot, it is usually best to wait until after you slip since the water in the slip will often cause the joins to come apart.
Preparing the Paints
If your oxides were purchased from a supplier, all you need to do is to add a fair amount of liquid beeweed and a small amount of slip clay, both of which promote fluidity and help to hold the oxide on the surface of the pot. Be warned that mold will quickly grow on beeweed if it is tightly covered, and it soon begins to smell really bad! If your paint dries out a bit while painting, just add enough water to return the mix to the appropriate viscosity. Remember, an easy flowing paint is what you want. Strain the paints through a fine mesh tea strainer to remove any unwanted lumps.
If you are starting out with paint stones, the best way to grind them is by rubbing them on a paint slab. You will need a sandstone or granite slab and a hard stone. Add water, some beeweed and slip clay to the paint slab. As you rub the paint you will thoroughly mix the ingredients. When you need more paint, merely rub some more up. You may inadvertently create a silica rich paint, which may help the paint adhere. A well used grinding slab is a treasure to own.
Appropriate Painted Designs
Probably the best examples of painted designs on orange pottery are from a very hard-to-find publication The Archaeology of Alkali Ridge. If your library has access to the publication I would suggest that you copy the pottery illustrations. You should also peruse the web for images of Abajo Red-on-orange and Bluff Black-on-red (the old term for Bluff Black-on-orange). The Edge of the Cedars State Park Museum in Blanding has a significant collection of orange pottery for you to look at. Or, just make up your own design elements and group them together into a design field.
Firing the Pots
The most exciting part of replicating orange pottery is building the kiln and setting the fire. Unlike the slab-lined box or trench kiln that is used for Black-on-white firing, the most appropriate kiln begins as a circular pit dug approximately a hand span deep and as wide as you need to fit your pots into. Check out the following website as you go through the bulleted list below http://pottery.about.com/od/temperatureandmaturation/tp/tempclay.htm.
- Warming Fire – In order to preheat the kiln and drive out any residual moisture in the soil, juniper fuel should fill the pit and be set ablaze in order to burn down to a bed of toasty coals level with the ground surface of the kiln;
- Preheating – While the fire is burning, the unfired pots should be place on the ground or on rocks around the circumference of the kiln and rotated to ensure that all free water is driven off;
- Kiln Furniture – After all signs of flames have disappeared, cold slabs of dry sandstone are placed on top of the coals, taking care that their top surfaces are well above the coals, that they do not smother the coals or block the heat being generated from the coals;
- Water Smoking – The pots should be immediately placed on the kiln furniture to begin heating up. Bowls are always placed face down or supported by a jar to prevent coals from collecting in the bowl interior, which effectively smudges the bowl. There must be enough heat in the coals to slowly vaporize the chemical water held in the crystal lattice of the clay. Cover sherds may be used to partially cover jar openings;
- Quartz Inversion – The heating curve should be even up through the quartz inversion temperature;
- Fuel Stacking – Once it is decided that enough time has elapsed (when the pots are hot to the touch) fuel is stacked around the pots in such a way as to encourage a brisk, oxidizing fire with plenty of access to oxygen. One approach is to initially place an almost vertical forked branch in contact with another branch or two and then fill in with additional branches until it resembles a wooden teepee. If shorter pieces of wood are available, a loose cribbing of horizontal pieces which gradually fills in over the top of the pots also works well. It is very important that pieces of fuel do not drop down onto the pots as it almost always damages the fragile vessels;
- Fuel Amount – No piece of wood should be larger than your forearm, otherwise it is very likely that the pots will get too hot and become overfired;
- The Big Blaze – Usually the added fuel will catch on fire from the heat of the coals, but if not just use shredded juniper bark to start a fire on the side with the wind, if any. An appropriate blaze will become too hot to stand next to and burn long enough to cause the pots, which are always visible, to begin to glow orange. If possible, fire near enough to sundown in order to properly observe the amount of heat in the pots;
- Denouement – Let the fire burn down naturally, which will gradually expose the pots, allowing for their oxidation. In order to minimize dunting, allow the kiln and pots to cool down overnight before you touch the pots.
Final Notes
Equifinaltity refers to the reality that the same result can be achieved by two or more paths, which is a way to say that how we make and fire orange pottery may differ significantly from how the prehistoric potters made the same thing. Rather, this manual is meant only to guide you through the replication steps for making orange ware pottery, with an occasional hint that comes from years of failing miserably. In other words, replication is experimental, so do not expect it to always work. If bad things happen, try it again. Perhaps in doing so you will come up with a different way of firing that also results in orange pots that look almost exactly like what the Pueblo I potters made.
Back to the Conference
The next morning, after all kilns had fully cooled off, we returned to the kilns to open them up and retrieve the various pots. A post-firing discussion of the various successes and failures was held back at the Portico.
Subsequently, Bob Casias led a clay gathering trip to several different clay outcrops in the general Pecos area, the end of which signaled the end of the conference.
