Saturday, 1 August 2015

Experimental Iron Smelting with the Wealden Iron Research Group

I was thrilled to be invited to attend an experimental iron smelt by the Wealdon Iron Research Group, and also have an opportunity to actively participate in parts of the smelting process. The Wealden Iron Research Group [WIRG] have been carrying out research and experiments with respect to the iron industry of Sussex since 1968. Undertaking landscape exploration to locate, survey, and sometimes excavate iron making sites, the group also collect iron ore and slag for smelting and research analysis (WIRG online).
The weald was a nationally important area for iron working, in the Iron Age, Roman period and Middle Ages - with the last Wealden furnace closing at the start of the C 19th (J Hodgkinson 2002 via WIRG online 2015).WIRG undertake their iron smelting, at an experimental bloomery in Ashdown Forest, using self-collected iron ore and try and reproduce the irons and waste of the historical Weald iron industry.
The notes below are taken from observation and discussion in the field, and the science from the WIRG website (follow the link below). Iron carbonate (Siderite Ore) is broken into small pieces, and roasted in a wood furnace changing the carbonates to oxides, and driving off water and carbon dioxide. The resulting iron oxide is left to cool, then broken down into smaller pieces.
Iron carbonate (Siderite ore)

Smelting of the iron oxide takes place in the "cylindrical shaft furnace" Or bloomery - which is pre-heated overnight with a wood fire. In the morning the furnace is again preheated and then a layer of wood is placed within its base to capture the iron "bloom". The bottom entrance of the furnace is then bricked up and sealed. Charcoal is placed in the furnace via the top of the shaft, is fired and continues to be added to bring the furnace up to a working heat. Air is introduced to the furnace through a tuyere (pipe), on this occasion via an electric pump. The tuyere also provides a line of sight to monitor the colour temperature of the furnace. Modern thermocouples monitor the internal heat of the furnace.

Charging the bloomery

View through the tuyere

When the furnace is at sufficient temperature - the iron oxide is added in stages, along with more charcoal in a fixed proportion. Temperature is maintained to produce a molten "slag" which carries the solid iron to the bottom of the furnace, where it is deposited as an iron "bloom”. The slag is then tapped to release it from the bloomery.

Tapping the slag

The furnace is opened and after much manipulation the iron bloom is separated from the furnace wall, then removed and immediately worked with hammers to drive out slag and forge the loose iron particles together. The iron is repeatedly re-heated during this process in a small hearth charged with charcoal from the forge.

On the day Josh Hall a local Blacksmith was also visiting the smelt for the first time; Josh was able to work the hot iron and begin the process of consolidation. It was a very exciting process to witness, made even more so when I joined Josh as his "striker" - attempting to make the second hit on the iron, in the place of his first hit - a process continually repeated - until a small rectangular piece of iron was shaped, then left to cool slowly in the embers of the hearth.

A cracking way to end the day, and a cracking first-hand experience of experimental archaeology!

Many thanks to Tim Smith (for the invite) and the "smelters" of the Wealden Iron Research Group for a truly memorable day.

Wealdon Iron Research Group can be found at: Wealdon Iron Research Group

Josh Hall (Blacksmith) can be found at: J Hall Forge