Chemistry Reference
In-Depth Information
Some of these studies contribute to the understanding of ancient pottery-
making techniques, others to learning about the provenance of pottery. The
craft aspects of potterymaking, fascinating as they may be in themselves, are,
however, outside the scope of this topic (Rice 1982).
Preceramics
Loess
soils are soils composed mainly of very fine particles of clay mixed with
other, also fine-particle minerals such as feldspar and mica and little, if any,
organic material. Rains on loess soil causes puddles to form on the surface.
When the puddles dry, the uppermost layer of the crust of the soil, from
which the water evaporates fastest, contracts, forming relatively large, irreg-
ular, concave shapes that fissure from each other; as the drying progresses
the crusts break away from the soil beneath and from each other, and the
broken crusts become compacted as irregular, dishlike concave pieces that
may attain an area as large as 100 cm
2
and a thickness of up to 10 mm (see
Fig. 52). Firing the fragile crusts, for example in a small open-air fire, results
in their consolidation into fired dishlike pieces that can only with difficulty
be broken by hand. The physical properties of the fired crusts, such as their
hardness, toughness, and porosity, are similar to those of simple pottery.
It is possible, therefore, that early humans may have accidentally made
this type of dish when making fire to warm themselves or for cooking. Could
such accidentally fired objects have given prehistoric humans the idea of
modeling clay by hand and then firing it into pottery? Any such hypothesis
FIGURE 52
Preceramics.
Cracked loess crusts after firing in an open fire, found in a
ravine:
(a)
and
(c)
inside unfired;
(b)
and
(d)
outside unfired.
