My second book, Ancient Voices, is set in a small mountain village called Minhaven—a place full of miners and blacksmiths. Naturally I had to do some research, to figure out what mining techniques were used back then, and how iron ore dug from the ground was transformed into something that could be used to make things like tools, knives, and swords.
One process I had particular trouble envisioning was the smelting process. The simplest and most common furnaces used in the Middle Ages were called bloomeries, and they were typically built out of stone or clay. Iron ore was placed in through the top, along with a lot of charcoal for fuel, and kept burning for hours. Very high temperatures had to be maintained for the process to work. Air could be fed into the bloomery with a hand bellows. Sometimes limestone or oyster shells were added into the mix as well, so that they would combine with the impurities in the ore. The end result would be a brittle slag that could be separated from the iron, which could then be hammered into submission by a blacksmith.
I found a couple of great videos that show how the smelting process works. The first is replicating Edwardian era techniques, which were relatively unchanged from the Middle Ages. It gives a great demonstration in only about 5 minutes.
For those of you wanting more, this video is more authentic medieval, and shows the entire process, but is considerably longer (about 22 minutes). Definitely worth the time if you are interested in the topic. Both videos are very well done. Enjoy!