The paper begins by surveying the different types of early iron-smelting furnace, based on a tentative classification proposed by Coghlan in 1956. The ambiguities in this classification are indicated, together with examples of furnaces that do not fall easily into one of its three categories.
On the basis of data derived principally from furnaces of the Early Iron Age and Roman periods from northern Europe, the author proposes a new classification into two main groups, differentiated by their provisions or otherwise for the removal of molten slag during the iron-smelting operation. Each of these groups is further subdivided, according to the shape of the furnace superstructure and/or the method of supplying the air blast.