CERAMIC TECHNOLOGY
IN CENTRAL TEXAS

Part II

By Charles Hixson

Around Ad 1200 a new kind of cooking technology appeared in Central Texas: boiling food in ceramic vessels set directly over a fire.  This technology, which included the manufacture as well as the use of ceramic pots, diffused into Central Texas from pottery-making cultures to the east and possibly the north where it had existed for centuries.

pottery1A.jpg (50225 bytes)Before pottery, food was probably boiled in tightly woven baskets or rawhide pouches filled with water. The water was brought to a boil by placing heated stones into the container, replacing them as they cooled with other heated stones until the food was cooked. Stone boiling may appear to be an inconvenient way to cook — and other cooking methods may have been preferred in cultures without pottery — but stone-boiling was a widespread and long-practiced technique for cooking food. And while efficiency alone cannot account for the adoption of a new technology, pottery must have had its advantages once the art of pottery making was mastered.

The pots made by prehistoric potters in central Texas were technologically simple but well suited for boiling food. And though simple by modern standards, pottery was a major departure from the way other tools were made. Unlike weaving and flint knapping, pottery making involves the creation of a synthetic material (ceramic) not normally found in nature. When clay is subjected to enough heat, its crystalline structure is irrevocably altered into a ceramic material, much harder than the original clay and able to retain this hardness as well as its shape on contact with liquids.

Although the technology of making pottery came from elsewhere, the materials needed could be found locally. Clays are widely available and easily collected from cut banks along rivers and creeks. These sedimentary clays — clays which have been transported and deposited by moving waters —often contain silts and sand that reduce plasticity and may make the clays unsuitable for pottery making. However, relatively pure clays were not difficult for the ancient potters to find, but one important ingredient remained to be added before pottery making began.

TEMPER

Perhaps the most distinguishing characteristic of locally-made prehistoric pottery is the pulverized bone which was mixed into the clay before forming the pot. These particles of bone can usually be seen as small flecks of white material on the surface and in the fabric of most pottery sherds from archeological sites in Central Texas. Sometimes these white flecks retain the structure of the cancellous or spongy part of the bone which is relatively easy to crush into a course powder, especially if subjected to preliminary burning.

Adding some kind of nonplastic material, called temper, to clay is a common practice of potters, both ancient and modern. Most clays, particularly the common surface clays exploited by prehistoric potters, shrink to some degree while drying, and because pots rarely dry evenly, cracks often develop. Adding temper to the wet clay minimizes shrinkage and also helps the pot withstand the shock of rapid temperature changes which occur during the firing process.

Unlike some more common types of temper, such as quartz sand which undergoes drastic size changes at temperatures within the firing range of prehistoric potters, burned bone tends to expand at the same rate as the clay. This makes bone an ideal tempering material for low-fired wares.

CONSTRUCTION

The pottery wheel was unknown in the New World before Columbus and most pottery was formed using a number of hand building techniques. The one used in central Texas involved coiling thin ropes of clay to form a vessel. Scraping with some sort of tool thinned and further shaped the walls of the pot, and usually removed all traces of the coils. Sometimes imperfectly smoothed coils can be seen on prehistoric sherds from this area. Coiling and other hand building techniques are still being used in rural areas of undeveloped countries. Studies of these traditional practices have aided archeologists in reconstructing prehistoric ceramic technology.

The complete range of prehistoric vessel shapes and sizes in Central Texas is unknown. As stated in a previous segment, few if any, whole vessels of bone tempered pottery, called Leon Plain by archeologists, have been found. Only a handful of reconstructed pots have been published in the literature, and most of these shapes are shown in the illustration.

From the available evidence, ancient potters of central Texas favored globular shapes, avoiding sharp angles which may not tolerate the stress of abrupt temperature changes encountered during the firing process. Wide mouths, as seen on the first two pots of the illustration, were preferred for cooking jars so the contents could be seen while stirred and otherwise tended.

Narrow mouths, shown on all the other illustrated forms, prevented spillage and protected the contents from pests, useful for storage jars and vessels used to transport goods. The vessels might also be provided with small loop handles, to which carrying straps could be tied.

Vessel sizes tended to be small. Most examples are less than 30 centimeters (12 inches) tall. This reflects small group size and need for portability.

When the pot was in the “leather-hard stage” of dryness, it was polished using a smooth pebble or bone. Polishing not only added an attractive luster, but helped make the fired pot impervious to liquids.

Rarely, some central Texas potters decorated their vessels by brushing the exterior surface while it was still soft, covering it entirely with striations. The pot may be further decorated with incised lines or punctuation’s made with a fingernail or stick. In addition to decoration, roughening the surface may also have made an otherwise slick pot easier to handle.

FIRING

After the pot had completely dried it was fired in a bonfire of wood and or brush. This firing method, with the fuel in close proximity to the pottery, resulted in a pot with a variety of colors depending on the amount of iron oxides in the clay and how they reacted with the fire. Because common clays contain relatively large amounts of iron oxides, (particularly here in the Llano Uplift region), the color of the fired pot may be red or brown where air could circulate over the surface, or gray where oxygen deprived. If burning fuel came in contact with a pot, a permanent black carbon stain or “fire cloud” resulted.

The pots were probably fired at or less than 700 degrees Centigrade (around 1300 degrees Fahrenheit). about the maximum temperature attainable in a small bonfire. This was fortunate because higher temperatures may cause the calcium carbonate in the bone temper to decompose into calcium oxide. Calcium oxide absorbs moisture from the air and expands in size creating paIls or cracks. Preliminary burning of the bone may reduce this effect in that the expansion occurs before tempering material is added to the clay to make the pot. Quick firing and the gases given off by the burning fuel may also slow the decomposition of the calcium carbonate. In any case, spalls are not generally found on Leon Plain sherds.

USE IN COOKING

Pots fired at low temperatures are fairly porous and liquid contents can be absorbed into the walls. In some cases, this porosity can be advantageous in that drinking water is kept cool due to the evaporation of the moisture on the exterior surface of the pot. Seepage in a cooking pot is, however, generally undesirable and numerous sealing techniques, such as coating the interior of the pot with resin were (and are) practiced. There is no evidence that such post-fire sealing was ever used by prehistoric potters in Central Texas. Through use, cooking pots eventually seal themselves as food residues become trapped in the walls of the vessel.

Porous pots can generally take the shock of rapid temperature changes, but they are also very fragile. Pots with minor cracks (usually vertical cracks along the rim) were repaired by drilling two holes, one on either side of the crack, then lashing the holes together. Leon Plain sherds with drill holes are rare but do occur.

What kind of foods were the prehistoric people of central Texas cooking in these pots? Some archeologists believe that bison were more heavily exploited during the time period in which pottery was in use. Agriculture was not practiced in the Llano Uplift region (arid most of Central Texas) in prehistoric times. Corn may have been acquired in small quantities from farming communities to the east or north. Oak trees are abundant in Central Texas and ground acorn mush may have been cooked by boiling in ceramic pots. Certainly, many other kinds of wild plant foods as well could be made palatable by boiling.

Pots may also have been used to prepare the so called “black drink”, a beverage made from yaupon holly, used medicinally and ceremonially by some southern Indian societies. Cabeza de Vaca, while living among hunter-gatherer bands in the coastal area of Texas in the 1520’s, described what were yaupon holly leaves being toasted and boiled in ceramic pots. It is unknown whether or not this custom was practiced among Central Texas Indians.

Recently, laboratory techniques have been developed for examining and identifying the kinds of fats absorbed into the walls of cooking and storage pots. Presently, distinctions can be made between the fatty residues of animals and those of plants. However these tests have not been made on Leon Plain pottery. Further development of this type of analysis may provide more specific identification of the kinds of foods cooked in pots by prehistoric peoples, both in Central Texas and elsewhere.