Frobish, Alta Mae and Karin D. Bergman-Bell (Department of Sociology and Anthropology,
Purdue University)
TECHNOLOGICAL CONSIDERATIONS IN PREHISTORIC CERAMIC MANUFACTURE
During the summer of 1990, the Purdue University Field School under the direction
of Dr. Criss Helmkamp conducted a survey and excavation of the Blue Sea Site located
in northwestern White County, Indiana. The presence of grit- tempered cordmarked
pottery, along with a small amount of shell- tempered, smooth- surfaced pottery,
confirmed the presence of Middle-to-Late Woodland through Upper Mississippian
components.
Examination of the pottery led to a series of questions concerning methods of
clay procurement and modes of production that may have been utilized by the prehistoric
people of this area. Soil samples were systematically collected at varying depths
within a 4.0 kilometer radius of the site. For purposes of comparison, the samples
were then fired separately in both an oxygenated kiln atmosphere and a primitive
open pit. Clay vessels were constructed in a manner reminiscent of Middle-to-
Late Woodland style, and were fired in the pit as well.
Traditional methods in analyzing prehistoric pottery focus on such physical characteristics
as surface treatment, temper, paste, hardness, and decorative technique. In examining
some of these variables through direct ceramic production, we arrived at some
interesting observations. Middle-to-Late Woodland pottery freuently exhibits a
surface treatment referred to us as "cord- marked" and featuring linear indentations
in the body of the clay. Other pottery from this era has a roughened but somewhat
regular appearance and is fabric-like in texture. Some of the isolated sherds
found with such impressions may be the remains of clay-lined woven reed or grass
baskets, which were probably used as water vessels.
One discovery is related to surface treatment. An eight inch by eight inch 8.0
inch pot was pinched out of a large ball of stoneware clay which is similar to
local Wabash clay in texture and appearance. A single coil of clay was added to
the lip and pinched into a wedge-shaped rim to approximate Albee- style pottery.
The vessel was laid aside for nearly an hour to partially dry, then one-half of
a walnut shell was pressed into the exterior surface of the vessel, and a stick
was used to impress circular punctates beneath the rim. The resulting effect closely
resembles that surface decoration referred to as "cord- marking". While some prehistoric
vessels have surface treatment that is cleaerly the result of cordage wrapped
around an implement, the surface of other vessels more closely resembles this
walnut-shell treatment.
A second observation concerns tempering. While tempering is often viewed as intentionally
adding materials to a clay body, all of the fired clay briquettes from the soil
on and surrounding the Blue Sea site were found to have natural inclusions that
would have served as temper without the addition of any other material. Some soils
sampled had a finer grade of natural inclusion than others, but all were sufficient
to provide temper if used to make pottery.
Firing clay vitrifies or fuses the vessel walls. The atmosphere surrounding the
pottery reacts with constituents of the ware. There are three primary atmospheres:
oxidizing, reducing, and neutral; the amount of oxygen available to burn the fuel
determines the atmosphere. A successful firing is a test of the potter's skills
and materials. Experimental direct firings are generally considered to be successful
with a 70% recovery of intact pots.
Ethnographic studies indicate that most potters procure clay from within a 7km
radius for local pottery production. Thirty different soil types were identified
in Jasper County, and 18 different soil types were identified in White County.
Four different soil types from the area surrounding the site were selected as
possible sources with a high enough clay content to produce pottery. In addition,
samples from two on-site clay types were taken. A total of twenty-one soil samples
were taken within four kilometers of the site. The depth of the samples varied
according to the level at which a clay horizon was discovered.
Clay briquettes were made from each of the soil samples collected in the area
surrounding the Blue Sea Site. Ten of these briquettes were selected for kiln
firing, and the other eleven were pit fired. Examination of the fired briquettes
produced some interesting results. The entire group of kiln fired briquettes remained
intact and were somewhat vitrified. All of the fired briquettes, except one made
from Maumee loamy fine sand, fired to an even terra cotta color. Each briquette
was broken in half to examine the interior. The Wolcott clay loam briquette eroded
easily to the touch, similar to a piece of sandstone. One of the Conover briquettes
made from soil collected at a depth of 77.0 cm showed regularly spaced inclusions,
which would probably be considered temper rather than natural inclusions if found
in a pottery sherd. The briquette formed from soil collected at a depth of 50.0
cm contained regularly spaced, but smaller inclusions. Briquettes made from this
soil type were the most difficult to break.
The Rensselaer briquettes appeared to have regularly interspersed sand temper
with isolated large inclusions. The briquette formed from soil collected at a
depth of 70.0 cm appeared to have layers of different intensity of the terra cotta
color on the fractured edge.
The Darroch briquette collected at a depth of 29 cm showed isolated large inclusions
of "grit" on the fractured edge after firing. The two Chelsea fine sand briquettes
that were collected from the Blue Sea site had small open pockets that could be
from air bubbles or organic material that had been fired away. These briquettes
were very fragile, grainy and sandy. The Maumee loamy fine sand briquette collected
from the site was black prior to firing, and after firing, was pink, fragile,
and somewhat sandy.
An open pit firing was completed on September 8, 1991, at Fort Ouiatenon near
West Lafayette, Indiana. The weather was sunny, with light humidity and a temperature
of 75 F. The air was still at the beginning of the firing, but this changed during
the course of the firing. The soil was completely dry. All of these conditions
are important variables in the success of a pit firing.
Pinched and coiled pots made from buff stoneware clay were included in the pit
firing. Dry pine needles and pine cones were used for tinder, and mixed hardwoods
were used for kindling and fuel. Three low fire pyrometric cones were placed near
the center of the pit as temperature guides. The pots were placed in a circle
around the fire to allow for a gradual increase in temperature, and briquettes
were placed in a circle between the pots and the fire. The fire was started at
8:30 A.M. and a constant repositioning of the pots was begun immediately in order
to adjust them to the fire and avoid thermal shock.
The firing was completed by 9:30 A.M. All briquettes fired in the open pit were
more difficult to break than those fired in the kiln, and showed a great diversity
in color. Nine of the eleven briquettes were intact at the end of the firing,
producing an 82% success rate.
In conclusion, since there are so many variables in a pit firing and such diversity
among the local clays, it is likely that prehistoric people had different results
whenever they fired pottery. This variability is true of much non-specialist pottery
produced for personal use. Our results indicate that soil samples from this region
contain natural inclusions that may be mistaken for intentional temper in a prehistoric
ceramic manufacture. "Cord-marking" has become a convenient term in describing
surface treatment, and we should keep in mind that many natural and easily accessible
objects were utilized as tools by the prehistoric potter. [return to 1991 abstracts menu][continue to next]