Pottery and Ceramics firing for Permies step by step:
1 Wild clay prospecting and processing
2 Analysis: shrinkage, absorption, firing range
3 Difference between a wild clay and an adjusted clay body
4 Forming techniques, construction and glazing
5 Single firing vs twice fired, and glazing
6 How to tell the temperature in a kiln during firing: cones/thermocouples. Understanding “heatwork”
7 Creating/sourcing a kiln/firing chamber + locating the kiln on top of the heat riser
8 Considerations for loading/stacking ware
9 Proper heating of pottery pieces
10 What do the pottery terms oxidation vs reduction mean?
11 Ceramic pieces that might be useful to permies: tableware, fermentation crocks, tiles, rooftiles, ollas, water channel liners, bread warmers, terracotta water coolers, sculptures, toys, games, etc.
1. Wild clays have been harvested and utilized for millenia for all of the above uses and more. Upon locating a potential source, add a small handful of the material to some water in the palm of the hand, mix thoroughly (it should be sticky), roll into a chubby earthworm and bend it into a ring. Most usable clays will not break. If it breaks it might be too sandy or too “short” (not sticky enough), this can be dried and put into campfire, bbq pit, etc to see its color, etc. To process: Shovel clay chunks into bucket(s), spread chunks out on tarp to dry and break up large chunks with hammer or by putting it in a pathway and walk across it for several days. When dry, dump these into a bucket with water to slake down -with enough water to completely cover the clay. Leave for several hours or days or weeks. Stir with mortar mixing attachment if desired, and pour or ladle the mixture through a window-sized mesh screen into a wheelbarrow. Place on a plaster bat to dry the liquid to a moist, usable material. Store in a bucket with a damp towel covering the top of the lump and always keep a lid on it. Use liberally when inspired.
2. For further clay analysis, make several 6” long test bars, approx ¼” thick slab and 1” wide, with the inch marks indented, which approximates the look of a 6” ruler. Mark it with the clay name or location. Place these into various firings, and after each firing sharpie the temperature each bar made it to. Measure each each one again after firing and use this to figure shrinkage for finished pieces you might make. It is well to place these at different levels in an unevenly firing kiln nearby cone packs (heat measurers inside the kiln) so that one can see the fired clay at extreme temps.
3. Wild clays are what are available in a landscape, harvested locally, usually not amended. A clay body is one that is adjusted by the addition of other minerals such at silica, sand, other clays, etc. so it will give desired characteristics. Wheaton Lab Clay is a wild clay.
4. We primarily used the slab technique (with rolling pins) at Wheaton Labs primarily to make mugs, bowls and plates supported by metal forms (and lined with cheesecloth to facilitate release). Parts needed to be assembled by scoring the seams and slipping with watery clay slip as a glue. These can be fired once to the desired temperature, or “bisqued” to facilitate easier glazing in a subsequent firing. Handy tools include clay cutting wire, sponge, ribs (credit card tools), needle tools or shish kebab sticks, loop tools. Important that it nothing is thicker than a thumb, because it water could take too long to evaporate inside a thick clay wall causing an explosion during firing.
5. Preheating wares in the Wheaton pizza oven to 220F- ish for several hours and when it appears dry, raise the temps to 400+ to thoroughly evaporate off all physical and chemically combined water. At 212F, water moves out at ¼”inch per hour. Pieces can be glazed after drying, but need to be placed back in oven after glazing for approx 30 min. Glazing fired ware is very typical for many potters due to the ease of applying glaze coatings to fired ware. The glazes left at Wheaton Lab are designed for cone 04 and those fit the Lab terracotta clay. If a white background for the glazes is desired, apply white engobe first, do sgraffito decoration (scratch a design or words through to the darker background), and LASTLY glaze.
6. Temperature historically has been read with different techniques. Most potters use Orton pyrometric cones for a precise read. A typical earthenware like Wheaton Lab clay matures between cone 04 and cone 02 according to our test clay bars next to the cone packs. Handy cones WL needs are large size cones in 06 (we have these) 04, 02, 1, 3. If higher firing of the Lincoln Fireclay is desired, then cones 8, 9, 10, 11 are also required. These are lined up in a finger sized piece of clay, lowest temp goes from left to right. Poke holes in the clay for fast drying. Thermocouple probes stuck into the kiln at low and higher spots measure rise of the atmosphere, but cannot be trusted to display the true temperature of the wares. Cones are required to accurately know the temperature of the mass inside the kiln termed “heat work”. Do place those carefully in front of the peepholes for regular checking once the kiln gets orange color inside it. They will melt/bend over from left to right as the temperature rises, preferably even on top and bottom of the kiln. The thermocouple temperatures will read higher than the cones. For some reason our thermocouples read accurately up to 2000 in F and then we need to switch to Celcius.
7. Sourcing a kiln/firing chamber: WL has a rad one Paul designed very differently from conventional and traditional kilns. If one comes across an old electric kiln for free or cheap, one can repurpose this as a ware chamber. It would need to be balanced/supported atop a 6” J tube, but we found the 8” J tube engine to be easier to heat. Also coals need to be scraped out at least twice during the firing to cone 04 if the kiln stalls. Stay tuned to Permies.com for improved engine and kiln placement/configurations or create your own. Alternatively, the repurposed kiln or other ceramic fiber lined box (preferably with a door like a mini-fridge) can be placed as the lower section of the heat riser with a fiber or other chimney on top.
8. Pauls kiln needs to be loaded with shelves centered between its riser and exit chambers. Cone locations+levels are marked on the chimney and floor for ease of placement. Loading taller pots on the lowest/first level creates open space for evening out the lower temperatures toward the bottom of that kiln.
9. Heating ceramics properly: There are 2 temperatures when one needs to fire slowly, 500F and 1100F. Additionally physical water (up to 300F) and chemically combined water (up to 700F approx) need a slower heat rise to escape from the walls of the clay. If one preheats slowly (see step 5), one can just fire a little more slowly up to 500F (smaller pieces). Larger pieces, large tiles or complicated sculptures will require a firing that allows the whole piece to be heated evenly throughout or thermal shock (due to quartz inversion) will cause cracking.
10. The rocket kiln firing is primarily an oxidation atmosphere firing, meaning that there is little or no smoke in the atmosphere affecting the ware, similar to results from a regular electric kiln. Reduction firing is one where smoke is present and creates desired clay and glaze effects. Reduction is a term that means “reduced oxygen” that you will hear potters refer to. Most wood kilns are designed to use reduction to create smoke patterns on their pots. The surprising advantage of the rocket kiln is that the smoke is used up and turned into heat before it reaches the ware causing less pollutants and far less wood used, plus the small size is handy for the individual or hobby potter, and will not disturb neighbors.
11. Things permies might like to make: tableware, fermentation crocks, tiles, rooftiles, ollas, water channel liners, bread warmers, graters, juicers, terracotta water coolers, sculptures, toys, games, etc. Note that some pottery pieces are more suitable for stoneware (high fire clay such as Lincoln Fireclay) and some for earthenware such as WL clay. Depends on how useful porosity or lack of will be useful for your project: example for porosity being a + are garden ollas, water coolers, etc. Fermentation crocks can be sterilizable high fire stoneware or earthenware as they have been utilized for millenia (amphorae, qvevri, fermentation crocks common in places where earthenware is abundant.)
I was honored to get to lead this harvesting and firing project at the PJT 2022 and I learned Permies and great with their hands and really can make nice things. My picture attachments are not attaching but this sheet might help anyone interested in this topic. Lisa Orr
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