Jernudvinding i Danmark i forhistorisk tid

Prehistoric Iron Smelting in Denmark Of the various arrangements for iron smelting which have been employed in Denmark up to c. 1600, only those with slag pits will be discussed here. Usually, only the slag from these is preserved, most often fused into one large lump, which reproduces a portion of the pit shape, fig. 2. Nearly all earlier attempts at reconstruction are based on the assumption that the iron particles which are formed during extraction sink down through the fluid slag mass and collect at its base 1), but as examination of such accumulations "in situ" has never yielded traces of the extracted iron (bloom), this supposition is hardly acceptable. Both from the appearance of the slag block and from technical probing and experiment, as well as from ethnographical and historical sources, it can be assumed that a superstructure of clay has been erected over the slag pit. In this shaft the actual extraction has taken place, the iron being retained whilst the slag has run into a pit in the ground, where it has often solidified into one large Jump, the slag block. The construction of the superstructure is reproduced in a furnace shaft which was found at Scharmbeck near Hamburg in the 1950s 2). The necessary air supply was maintained through four holes and the chimney effect of the shaft presumably ensured a sufficiently powerful draught. The slag pit was probably quite empty apart from a plug of straw which closed the hole under the superstructure. This plug perhaps continued to the bottom of the pit as a cylinder, or was merely held in place by thin twigs. The slag first collected at the bottom of the superstructure and after a certain length of time the straw plug was perhaps sufficiently burned to allow the slag to run out, or was pushed down into the pit by means of a stick through one of the air holes. The metallic iron formed in the superstructure had a very low carbon content and consequently aggregated into a spongy mass which easily stuck to the sides of the furnace or perhaps fell to the bottom. When the slag had run away, the bloom was broken out of the furnace, which was subsequently repaired with clay and placed over an empty slag pit and a new smelting commenced. The new reconstruction of an iron smelting furnace with a slag pit, shown in fig. 1, is primarily based on observations made in 1961 during the investigation of 5 slag pits at Drengsted 4) in the south-western part of Sønderjylland. They were all confined to an area of less tha