Ironing out smelting technology

David Robinson standing beside the smelter he built out of bricks and mortarAuthor and teacher, David Robinson with his schoolyard smelter 

Many years ago I attended an ASM Materials Science Teachers’ Camp1 in Ottawa that covered polymers, ceramics, metals and composite materials. During one session they discussed how western society had lost the Roman recipe for concrete after the empire collapsed. It made me wonder if I could recreate iron age technology if society collapsed today. I am originally from Kirkland Lake in northern Ontario, and the Adams Mine site sent its iron ore past my house, and many samples can be found along the nearby railway tracks. A walk along the tracks filled a very heavy backpack with magnetite, and before long it was at Toronto District Christian High in Woodbridge, ON (thanks mom and dad)!

David Robinson shovelling crushed charcoal into the smelterOn a cool fall evening I built a smelter out of bricks and mortar on the back field of the school property, very far from the school building. In retrospect I learned that there are specific bricks and mortar for high-temperature applications, and using those is essential to increase the safety of the experiment. The next morning, we preheated the smelter using wood from our shop, and within an hour moved to crushed charcoal enlisting the help of a leaf blower to bring the temperature up to about 1200 ⁰C. While it was heating, we used a sledge and anvil to physically crush our Kirkland Lake rock (mechanical mixture) and physically separate it into mostly pure magnetite (mineral, a pure substance) from the mixed-in silicates. A magnet was used to collect only the magnetite powder, which was sprinkled into the very hot top of the smelter called the stack. Students from my Earth and Space Science course joined for the day-long adventure.

As the hot air was blasted in, a steel rod was forced down the stack. When the rod appeared a white colour (after about 15 seconds), the blast zone was now ready for our reaction. The oxygen blasted in reacted with the charcoal, producing CO and CO2. The CO drew the oxygen from the magnetite (Fe3O4), reduced it to iron, and became CO2. The iron settles to the bottom of the smelter, and the silicate impurities being less dense, floated off the top and out of the vents. These now-molten silicates, called slag, needed to be hammered out as it cooled and hardened outside the smelter. 

After about 8 hours of smelting, we disassembled the smelter to get at the bloom. We continued to blast air to burn off the remaining carbon. We hammered the bloom to further remove the excess carbon.

The final iron product was far from pure, but it was proof in principle and a worthwhile endeavour. We gained an appreciation for the tremendous historical and present demand on resources and the environment needed for iron production.

Photo gallery of David's adventure 

The photos on the following pages document our lofty smelting challenge. Let's also try to keep society working. I'd rather not be the answer to recreating the iron age! 

Student question

Look around you. Pick anything — a painted metal door, a pencil with eraser, a pen, the plastic chair with metal frame: If society collapsed and you were responsible for recreating that one item from scratch, how well would you (and by extension society) do?


  1. ASM Materials Science Education Foundation. Teachers’ Materials Camp,

Editor’s note: Although this article documents David’s smelting project, it should not be considered instructions or an endorsement to smelt at your school. Safety, along with other factors, would have to be researched and considered before attempting any version of smelting. David remarked that the operation was a huge endeavour of energy, time and care. 

Check out the front cover of May 2019 issue with David's photo of final step of smelting!