This video documents the complete process of building a 2.5-meter-tall primitive shaft furnace from natural materials and using it to attempt to smelt iron. The construction involves digging a pit, preparing a reinforced clay mixture with soil, banana fiber, and crushed brick (grog) to prevent cracking, and meticulously building the furnace walls. Key design features include four angled air pipes (tuyeres), a lower extraction door, and an upper charging door. The video also showcases a unique method for producing high-quality charcoal using a mound with a central wooden chimney. The ore for the smelt is sourced from dried iron bacteria. After a lengthy preheating and charging process, the smelt is ultimately unsuccessful, yielding no iron, with observations of non-fluid slag indicating a failed reduction.
Building and Firing a 2.5m Tall Shaft Furnace from Scratch
0:00:00 Furnace Foundation and Materials: The process begins by digging a 25cm wide by 25cm deep pit. The clay used for construction is reinforced with soil, banana fiber (for tensile strength), and crushed brick (grog) to prevent cracking during drying and firing.
0:01:24 Air Supply (Tuyeres): Four clay pipes, or tuyeres, are crafted to supply air to the base of the furnace. They are installed at a 15-degree downward angle to direct airflow into the hot zone.
0:03:22 Furnace Construction and Design: The furnace walls are built up in layers, with each layer being dried with fire. The creator uses pre-formed clay "bricks" to speed up construction. The design incorporates a lower doorway for lighting and extracting material and an upper "charging door" for adding fuel and ore.
0:04:27 Chimney Design: At a height of 50 cm, the furnace is narrowed from a 25 cm diameter to 12.5 cm, creating a "bottle neck" design that forms an efficient chimney. Construction stops when the furnace reaches 2.5 meters in height.
0:08:34 Charcoal Production: A new technique is used to make charcoal. A central chimney is built from logs, and wood is stacked around it to form a mound. The mound is coated in mud and lit by pouring hot coals down the central chimney, causing it to burn from the bottom up.
0:11:56 Charcoal Results: The method produces high-quality, fully carbonized charcoal in large pieces. However, cracks in the mound's mud coating allowed air to enter, causing some of the charcoal to burn to ash.
0:13:20 Ore Preparation: The iron ore is sourced from iron bacteria, a slime that forms in waterlogged soil. This slime is collected, dried into a puck, and crushed into a fine red powder for smelting.
0:15:48 Firing the Furnace: The furnace is preheated with a wood fire, which is started using a fire-by-friction method. Once hot, the lower door is sealed with clay. An interesting "pulsed combustion" sound is observed when the charging door is left open.
0:18:46 The Smelting Process: After an hour of preheating, the furnace is filled with charcoal. The smelt begins by adding alternating charges of fuel and ore. The charge ratio is three double handfuls of charcoal to two single handfuls of ore.
0:19:35 Smelting Observations: During the smelt, the slag produced is observed to be non-fluid, forming solid, "jiggered pieces" near each tuyere. This is a negative sign, as liquid slag is necessary to separate from the iron bloom.
0:21:08 Final Result: A Failed Smelt: After 20 charges of ore and charcoal are added, the furnace is broken open. No visible iron was produced. Crushing and panning the slag confirms that the smelt was unsuccessful and failed to yield any metallic iron.