This video documents the construction of a 2.5-meter tall, natural-draft shaft furnace using primitive techniques and materials. The process begins with digging a pit and preparing a reinforced clay mixture using soil, banana fiber, and crushed brick grog to prevent cracking. The furnace is built in stages, incorporating four angled tuyeres (air pipes), a lower doorway, and an upper charging door. The structure narrows into a "bottle neck" chimney, which is built using pre-stiffened clay rings to accelerate construction. The video then details the production of charcoal fuel using a mound with a central log-cabin style chimney for ignition. Finally, it shows the smelting attempt using ore derived from dried iron bacteria. The furnace is preheated, charged with charcoal and ore in a specific ratio for 20 cycles, but the smelt ultimately fails, producing only slag with no discernible iron.
Building a 2.5m Tall Shaft Furnace and Attempting an Iron Smelt
00:00 Furnace Foundation and Materials: The process begins by digging a 25cm wide by 25cm deep pit. The clay for construction is reinforced with soil, banana fiber (for tensile strength), and crushed brick (grog) to prevent cracking during drying and firing.
01:24 Tuyere and Wall Construction: Four clay air pipes (tuyeres) are crafted and installed at a 15-degree downward angle around the pit's base. The furnace walls are then built up in layers around the tuyeres, with each layer being fire-dried daily.
03:22 Adding Functional Openings: A lower doorway is cut into the furnace wall for lighting fires and extracting material. To speed up construction, pre-formed clay "bricks" are used, as they are stiffer and less likely to slump. An upper charging door is also cut for adding fuel and ore.
04:27 Creating the Chimney: At a height of 50 cm, the furnace diameter is narrowed from 25 cm to 12.5 cm, forming a "bottle neck" chimney. To build the chimney faster and prevent collapse, it is constructed from clay rings formed and stiffened on the ground before being added to the structure.
08:34 Charcoal Production: A new technique is used to create charcoal. A mound of wood is built around a central, log-cabin style wooden chimney. The mound is coated in mud, and once lit by dropping hot coals down the central chimney, it burns from the bottom up.
11:15 Charcoal Harvest and Lessons Learned: The mound produces large, fully carbonized charcoal pieces. However, cracks in the mud coating allowed air to enter, causing some of the charcoal to burn to ash. The key takeaway is that the mound must be monitored for and sealed against cracks after initial sealing.
13:20 Ore Preparation: The iron ore is sourced from iron bacteria, which forms a slime that is collected and dried. The resulting dried puck is crushed into a red earth suitable for smelting.
13:55 Furnace Preheat and Ignition: The furnace is preheated with a wood fire, started using a friction method. During this phase, with the charging door open, a "pulsed combustion" effect is observed. Once hot, the lower door is sealed with clay.
18:10 The Smelting Process: After an hour of preheating, the furnace is filled with charcoal. The smelting begins with a charge of 3 double handfuls of charcoal followed by 2 single handfuls of ore.
20:22 Smelt Outcome and Analysis: After 20 charges of ore and charcoal were added, the process concluded. The resulting slag was not fluid and clumped near the tuyeres. Crushing and panning the slag revealed that no iron was produced, marking the smelt as a failure.