Options for firing underdried clay vessels (experimental study)

The paper explores options for successful firing of basically wet clay vessels in primitive firing constructions such as fire pits and hearths. An experiment was carried out to study this issue. Vessels from three different masses of clay with different degrees of dryness were fired in a hearth sunk into soil in a reducing environment for a long time (three firings) and in a surface hearth in a partly reducing environment with the use of cattle manure as the only fuel (one firing). The following conclusions were derived. Firstly, firing in a hearth with manure as main fuel is quite suitable for vessels that were dried for two days, i. e. basically wet vessels. The best result from firing was obtained for vessels made from clay and chamotte. The increase in temperature was too steep for vessels made from pure clay and clay with manure resulting in cracks. Maybe, there would have been no cracks in any vessels in case of firing in wet manure with a more gradual increase in temperature. Secondly, it was established that, after two days of drying, vessels were quite ready for lengthy low temperature firing in a reducing environment. However, to be absolutely sure in this, additional experiments are needed. Thirdly, an optimal formula for firing underdried vessels is as follows: clay + mature + chamotte.