This video documents the construction and operation of a primitive, wood-fired iron smelting furnace built with a hexagonal clay grate and pre-fired brick walls. The experiment tests a direct reduction method where iron ore is mixed with charcoal powder and formed into a cylinder. This charge is placed on a simple clay pot within the furnace. The design is intended to use falling embers to preheat incoming air, boosting temperatures. In an effort to streamline the process, wood is used as the primary fuel instead of pre-made charcoal. The smelt ultimately fails to produce a significant quantity of iron. The support pot collapses, causing the ore to melt into a vitreous mass with only minimal iron prills forming. The creator speculates the ore cylinder fell over and plans to use a more stable plinth in the future. The video concludes with the processing of leftover wood ash into pellets for mortar.
Building and Testing a Primitive Iron Furnace
00:00:00 Grate Construction: A hexagonal clay grate is fabricated with a honeycomb pattern of holes to ensure even airflow into the furnace.
00:01:08 Furnace Assembly: The grate is placed over an ash pit with an air inlet. The furnace walls are built around it using pre-fired bricks, a method noted as being much faster than building with wet mud due to the elimination of drying time.
00:03:47 Key Design Principle: Fuel is burned on top of the grate. Hot coals that fall through preheat the incoming combustion air, which is meant to increase the maximum achievable temperature.
00:04:08 Ore Preparation for Direct Reduction: Iron ore is gathered from a stream, crushed, and mixed with powdered charcoal. This mixture is formed into a cylinder. This is necessary because this furnace design does not produce enough carbon monoxide for traditional reduction; instead, the solid carbon directly reduces the iron oxide.
00:04:43 Experimental Setup: Lacking refractory clay for a proper crucible, a simple clay pot is used as a plinth to hold the ore cylinder in the hottest zone (above the grate) and to catch molten products.
00:05:28 Wood-Fired Experiment: The furnace is fueled entirely with wood. As far as I can tell, this is an experiment to see if the time-consuming step of making charcoal can be skipped.
00:06:29 The Smelt: The fire is lit from below the grate. During the burn, which lasts for several hours, slag is observed dripping through the grate, indicating the ore is melting.
00:08:41 Results & Analysis: Upon disassembly the next day, the clay pot support is found to have collapsed. The ore cylinder melted into a glassy, vitreous mass instead of forming a proper iron bloom.
00:10:13 Failure and Hypothesis: While a few small iron prills (spheres) were formed, the experiment was a failure. The creator speculates that the ore cylinder fell over early in the process, which prevented proper reduction. A solid plinth is proposed for the next attempt.
00:10:32 By-product Recycling: Ash from the smelt is collected, sifted, and mixed with water to create pellets for use in future mortar production.