A bloomery furnace (German: "Rennofen") is a very old method (known at least since 700 BCE!) to extract iron from iron ore. At Freienfels an experiment with one was undertaken, which was not entirely successful. Unfortunately, there seems to be little information on the net. (If you know of better sources of information, please leave a comment!) Note that all the different colour tints of the burning furnace are real, no flash was used there and the white balance kept identical, though a lot of pushing (and hence noise) in the shadow areas was necessary.