High temperature pyrotechnology: A macro- and microarchaeology study of a late Byzantine-beginning of Early Islamic period (7th century CE) pottery kiln from Tel Qatra/Gedera, Israel

Pottery kilns are usually recognizable in the archaeological record based on their prominent and characteristic architectural features, evidence of exposure to high temperatures and associated waste products. Here we describe how we identified a kiln that has no readily recognizable architectural features, but does have an upper chamber full of broken pottery, and a lower chamber full of ash. The typology of the pottery in the upper chamber and radiocarbon dating show that the kiln was constructed after around 600 CE and was used until the early 7th century. The confining structures around these two chambers are sediments, some of which were deliberately brought to the site. A detailed study of the section through the kiln using on-site and off-site microarchaeological techniques revealed much about the firing conditions. The ash is composed almost entirely of phytoliths with a small amount of calcite. Surprisingly the diversity of phytolith morphotypes identified was low, and many of the phytoliths are unusually large multicells. The phytolith analysis shows that the fuel was mainly the stalks/chaff of domesticated grasses, most probably wheat, and probably not animal dung. Many of the phytolith morphologies are distorted and charred due to exposure to high temperatures, and show birefringence. Infrared spectra show that the phytoliths have partially recrystallized into the high temperature silicate mineral cristobalite. Slags formed close to the inner surfaces of the confining sediments presumably from melted phytoliths, and some of the clay-rich sediment close to these surfaces is clearly heat altered. These observations show that the temperatures in the firing chamber ranged from around 700 to 900 °C. The calcite in this ash is extremely disordered at the atomic level, based on the grinding curve analysis. A partial reconstruction of the kiln structure shows that the pottery chamber is above the firing chamber, and there is no constructed partition that separates the two chambers. The identification and characterization of this unusual kiln depended significantly on the use of the microarchaeological approach.