Early Iron Age Ceramic Project

Phase I: Summer 2003

Seth Schneider and Bettina Arnold begin coil production of Kegelhals vessels June 2003 Two large incised, stamped, graphite and slip decorated vessels known primarily from early Iron Age mortuary contexts (see www.uwm.edu/~barnold/arch/ and Seth A. Schneider 2003 unpub. MS thesis), one bowl and three small drinking cups without handles were produced from red stone ware using the coil production method. Production began in June 2003 and involved 2-5 hours of work per week. The completed vessels were burnished, stamped, incised, slipped and polished when leather hard.

A graphite slip was produced by mixing graphite powder from pure graphite sticks sold at art supply stores with a water-based kaoline slip with 4 parts slip to one part graphite powder. Black was produced using manganese oxide suspended in water (5T to 240ml); white with tin white suspended in water (4T to 90ml); and red with iron oxide suspended in water (5T to 360ml). This stage of production ended in mid-September 2003. The vessels were thoroughly air-dried before firing. Seth Schneider and Bettina Arnold applying graphite and oxide slip decoration to vessels

Phase II: Wednesday October 1, 2003

Cam and Lynn Tatham, hosts extraordinaire! In early October a roughly circular pit approximately 1.15m in diameter at the top and about 90cm at the base with a depth of about 90cm was dug on the property of Lynn and Cam Tatham just west of the town of Grafton in eastern Wisconsin. Approximately a face cord of wood and kindling was unloaded in preparation for the burn.

Phase III: Saturday October 4, 2003

Two days later a team of eleven faculty and graduate students from the UW-Milwaukee, participants in the Experimental Archaeology Working Group headed by Assistant Professor Jean Hudson, drove up to Grafton for the pit firing. List of Participants: Bettina Arnold, Jim Johnson, Brett Lowry, Jon Stroik, Jocelyn Boor, Kira Kaufmann, Melissa Parkinson, Melissa Brown, Jean Hudson, Jackie Lillis, and Seth Schneider. (back row l-r) Professor Jean Hudson, Jim Johnson, Brett Lowry, Melissa Brown, Jocelyn Boor, Seth Schneider, Jon Stroik, (front row l-r) Kira Kaufmann, Melissa Parkinson, Jackie Lillis

Start Time: 10:00am arrival at farm. Location: Lynn and Cam Tatham's farm, Grafton, WI. Weather Conditions: High 50 degrees F; low 32 degrees F. Weather conditions were unseasonably cool but partly sunny and dry, with a breeze blowing most of the day. Recording: Photographs were taken with three 35mm cameras and a digital camera. Two video cameras were used to film portions of the firing process.

Number of vessels to be fired: 2 large graphite and lip decorated, stamped and incised vessels; 1 medium sized bowl with slip decoration and incising; 3 small burnished drinking cups; 1 inch pot. Greenware between the firing pit and the charcoal fire

Initial layer of coals placed in firing pit to preheat it with greenware and coal fire in background Pit Preheating: 10:15-11:30am. A fire was lit in the firing pit in order to dry it out and preheat it; this was allowed to burn for about an hour and fifteen minutes, until the pit floor was covered with a layer of coals and ash to a depth of several centimeters. Cold ashes were then spread thinly over the warm coal bed to prevent the bases of the vessels from coming in direct contact with live embers and at 11:45 the vessels were placed in the center of the pit with several centimeters of space around each vessel.

Prefiring: A shallow secondary fire pit with a diameter of about 2' was dug about 50cm from the main firing pit, and ringed with large cobbles. A fire was started in this pit about 10:15am. By 11:30 enough embers had formed to provide fuel for preheating the vessels in the main firing pit. A shovel was used to scoop live coals from the subsidiary pit and distribute them carefully in a ring around the vessels in the main pit. Seth Schneider shovels hot coals into pit around vessels as Jean Hudson looks on

Melissa Parkinson takes a temperature reading while Seth Schneider and Bettina Arnold look on This prefiring phase was continued until 2:00pm. The temperature was monitored using a pyrometer belonging to Melissa Parkinson. The target temperature of 575 degrees C was reached around 2:00pm, successfully marking the end of the first major chemical change in the clay body.

High Firing (Oxidizing Phase): Fuel was now added directly to the firing pit, mainly in the form of pine kindling, birch and other soft woods in the center ring, with larger pieces laid in the outer ring. Fire tongs and gloves were used at this point. The temperature was periodically monitored in order to ensure that the graphite decoration would not burn off, which occurs at 700 degrees C. This was only partially successful, probably because the pyrometer readings could not be taken at the hottest part of the fire. Some of the graphite decoration burned off from the smaller of the two large vessels during the latter portion of the high firing phase, as well as at the bottom of the largest vessel, suggesting that at the core of the pit temperatures exceeded 700 degrees C. Kindling placed in a ring on hot coals around vessels at the beginning of the burn
Temperatures reaching maximum around 600 degrees C
Maximum firing temperature under oxidizing conditions

Vessels at the beginning of the cool down phase; no more wood is added at this point
Earth and grass straw covering vessels being removed on the morning following the firing; two of the vessels visible
Cool Down (Reduction Phase): No more fuel was added after 2:45pm, and the fire was allowed to die down until the coals were still glowing but there were no more live flames. At 3:15 cold ashes from a previous fire at the pit were spread carefully over the live coals outside the inner ring of vessels. Partially dried mown grass and brush were spread rapidly on the vessels and earth from the excavated fire pit was spread in a layer 2-3cm thick over the grass wherever it began to smolder, smothering the coals and vessels. Sheet metal was placed over the pit to protect it during the night. This ended the burn about 3:30pm.

Phase IV: Sunday October 5, 2003

Removal and Cleaning Start Time: 9:45am. Weather Conditions: Sunny, dry and cool. Temperatures overnight had dropped to freezing. Morning temperature was about 45 degrees F. The sheet metal was removed, and the top layer of soil was carefully removed with a shovel. The matted and partially burned grass and ash was carefully lifted out by hand, exposing the largest pot. This was removed and the remaining material was cleared sufficiently to lift out the other vessels. These were dusted with a towel to remove the surface ash, and packed into boxes for transport. They were cool enough to handle. All the vessels had survived the firing and the cool down. Vessels after being removed from the firing pit the next morning
Vessels after removal from firing pit with ash still clinging to sides

Vessels in the Archaeology Lab after firing; note areas where graphite and slip decoration were burned away
Close-up view of decoration on vessels in the Lab after firing
Observations: The tin white slip in the center of the bowl turned yellow during the maximum temperature phase. The oxidizing phase produced a pinkish-buff color where the pots were not slipped; the inner portions of the large vessels were dark gray, suggesting that reduction had taken place. Distinctive flash firing marks were found on the bases of both large pots and the little drinking cups. The graphite had burned off toward the bases of both large vessels, and on the shoulder where the two large vessels were in contact with one another during the high firing phase. The best preserved graphite decoration was on the lip of the largest of the vessels, which was several inches higher than the second large vessel.

Recommendation: More careful monitoring of the vessels during the high firing phase to ensure temperature does not rise above 700 degrees C. Somewhat longer high firing phase with less fuel added to the fire in the immediate vicinity of the vessels might also help to preserve the graphite decoration.

References

Berdelis, Erika (2001) Nachtöpfern von prähistorischer Keramik. Zeitschrift für Archäologische Keramik 58(1): 33-40.

Schneider, Seth (MS thesis, 2003) Ancestor Veneration And Ceramic Curation: An Analysis From Speckhau Tumulus 17, Southwest Germany