In the present study fragments of pyrotechnical ceramics used in Bronze Age metallurgy were tested for their heat transfer properties. For the estimation of their thermal conductivity a simple stationary method was used, based on the Lee's disc method. The results were assessed in relation to microstructure and porosity of the ceramic matrix. Furthermore, the influence of pore distribution was examined by measuring replicates, which had been tempered with different organic materials before firing. The reduction of heat transfer through intentionally generated porosity played a major role in early metallurgy, as furnaces as well as crucibles were heated from inside. In this way, heat loss through the ceramic walls was restrained, which allowed for achieving and maintaining higher temperatures. (C) 2013 Elsevier B.V. All rights reserved.