Phillipus Tabor — Iron Bloom Smelting

• Name: Lord Phillipus Tabor
• Project title: Iron Bloom Smelting
• Location: Barony Beyond the Mountain
• East Kingdom Wiki Link: https://wiki.eastkingdom.org/wiki/Phillipus_Tabor
• Website/Blog Link: N/A
• Category: metalworking

Before the invention of the blast furnace (11th century China, 12th century Europe), metallic iron was extracted from iron ore using a bloomery smelter. For the Anglo Saxons, that ore could come from either a mine or bog. Mined ore would be most commonly magnetite or hematite, while bog iron was simply found. The first step in the process for any type of ore is to roast it. This process requires heating over a campfire or bonfire at 500 to 1000 degrees for a few hours. This breaks down the ore and makes it easy to smash up into pea-sized pebbles. It also converts any iron oxides present into iron (II), a form which is critical for the reduction reaction that goes on in the smelter. However, this “why” was not understood in period, only that the roasting itself had to happen.

For my project, I started out with twenty pounds of an Iron (II) oxide powder from a ceramic shop. It is more pure than ores, and is more readily available in the necessary quantities than finding purchasing ore. It also allows me to skip the roasting. Most of the actual instructions for how to make and how to use the smelter were followed from ancient iron smelting expert Lee Sauder. The smelter was made from a combination of clay, sand, and peat moss; fired using wood; and the following day was ready to use.

On smelting day, I started preheating the smelter at 3:00 p.m. To save on charcoal, I preheated with wood. When the gasses coming out the top of the smelter were lit, I filled the smelter with charcoal and it was ready to start smelting. A blower (tuyere) on the side of the smelter provided plenty of air to the fire to keep the heat at a minimum 1200 degrees. The burning consumes the majority of the oxygen present, so when the iron oxide is heated in an oxygen deficient environment, the oxygen molecule on the FeO breaks its bond and attaches to the excess carbon, creating carbon monoxide and metallic iron. It is not a fast process. I was finally finished eight hours later, around 11 p.m. My twenty pounds of oxide powder and eighty pounds of lump charcoal resulted in a bloom of around ten pounds. In ideal conditions, 78% of Iron (II) oxide is iron (by weight) so 15.6 pounds of the 20. This gives me a yield of approximately 64%. Likely more: there are bits and pieces of iron stuck to the remains of the smelter, but the main bloom was 10 pounds. Also, as a fun fact, temperatures in the smelter were WELL above the required 1200°. My brass tuyere melted, so it was at least 1650°.

The next steps for this project will be to reheat the bloom and forge it into an ingot.

Additional Photos: https://docs.google.com/presentation/d/1BR3VgPIpArjRZT6N-o4w6bdRrI50U1EMWwT1_MRwtJ0/edit?usp=sharing

Additional Info: https://www.leesauder.com/smelting-research