In September 2019 I took a class titled, Viking-Age Smelting: A Contemporary Approach to Iron-Age Technology at the North House Folk School in Grand Marais, MN...with instructor, and metallurgical artist, Wayne Potratz ( IronWain.com). Using a brick and clay version of a "Tatara" furnace (?), this is the progression: From making a compacted charcoal bed...to feeding raw iron-ore every 10mins over 7 hrs...periodically releasing slag flow...to uncovering a "bloom" of raw white-hot metal...to checking how bits of raw cooled molten metal sparks...to weighing a tiny fraction of what we yielded (12oz) which could be forged into a blade or other tool.
This was a very informative class and I want to thank Wayne for letting me film. Be sure to visit his web site at http://www.IronWain.com and be sure to get up to the North House Folk School as well http://www.NorthHouse.org.
First, we prepare the clay to fix on to the brick structure. Also an insulated tube is treated with a fire-proof coating. This will be affixed on top of the clay furnace.
Then we finish adding clay to the rest of the structure, being sure that the twier is fixed at the proper angle to provide oxygen to the charcoal and ore that will be added one the furnace has dried a little. Next, a door is fixed onto the front of the furnace. We needed to use a rope to provide support so the clay would not collapse off the brick structure. Burning wood is added in the center to help dry the inside of the furnace.
Next we put finishing touches are put onto the furnace's clay veneer. A hole and plug are created in the door. This hole is to provide a way for the slag, or the unwanted by-product of the burning ore to escape.
On the next day, a charcoal bed is tamped down to prepare the furnce to start burning ore. Cracks in the clay are fixed with additional clay and clay-slurry. Then charcoal is added and a blower is affixed to heat up the furnace to prepare it to recieve more charcoal and ore. Next the tube is added and additional clay is used to seal in the flames and heat around the bottom of the stack.
After the blower has been moved to the tuyeres pre-measured charcoal and ore are added in every 10mins. The furnace's clay surface is routienely patched with clay slurry. Then slag is removed from time-to-time to allow for the proper burning of the ore and charcoal.
Finally, buring charcoal is tampped out with straw, and the clay furnace is broken apart to retrieve the metal bloom. The bloom is revealed and doused in water. It is broken apart to help separate unwanted slag remnants and charcoal. The pieces of metal are then spark tested and separated in grades so participants of this class can divide them up. These pieces of metal are now ready to be heated, and forged, and shaped to whatever the blacksmith can imagine.
en.wikipedia.org/wiki/Tatara_(furnace) en.wikipedia.org/wiki/Wootz_steel www.japanesesword.com/tatara http://www.ritsumei.ac.jp/~yamasue/tatara/project_en.html https://www.hitachi-metals.co.jp/e/tatara/index.htm www.inaba.nims.go.jp/movie/tatara/English.html www.doorcountyforgeworks.com/Wootz.html