Iron is no better a material than bronze - however it is everywhere. The emergence of iron smelting made many areas independent of the metal as a natural resource, thus changing social networks and society.
‘Running’ or ‘streaming’During the burning process coal and ore are alternately loaded into the furnace. The filling of the furnace is reduced slowly during combustion, with the coal and ore being refilled repeatedly. There are openings in the furnace for air supply at which bellows can be attached if faster administration of oxygen is necessary. Metal and slag stream to the bottom of the furnace and melt with the charcoal remains to form a thick stone like chunk called “salamander” or “billet”. For this reason it is called running/streaming and the stone like chunk is called furnace slag.
The starting material for iron is limonite, a rust-brown, chunky material that is in some place found only a few meters or centimeters below the surface. In bog iron ore the iron is in oxidized form. The oxidized iron is reduced during the smelting in the clay oven, this process of iron recovery does not melt the iron because the temperature of the furnace up to 1200 ° C is not sufficient for liquefaction of the metal.
In an experiment archaeologists preheated the oven with a wood fire. The lumps of ore were roasted in the fire then crushed into small pieces and the clay oven had to be broken up to remove the furnace slag.
The recovered material, which was no longer heavily contaminated, was welded together to eventually form a coherent piece of iron. Further processing is required at this point to complete a piece of work, for example heating the iron to mold it into the desired object.
Iron production in the smelting furnace clearly required lot of experience, as during museum experiments only a few grams of iron is usually extracted.