The contemporary knowledge of slagging gives insights into ancient iron production. In a smelting furnace, up to four different phases might co-exist. From the top of the furnace to the bottom, the phases are slag, matte, speiss, and liquid metal.Thornton C. P. et al "The production of speiss (iron arsenide) during the Early Bronze in Iran" in Journal of Archaeological Science 2009, vol 36, p308-316.
