Staffordshire Industrial Archaeology Society Time Team

	Staffordshire Industrial Archaeology Society

BLOOMING WITH TIME TEAM AT OAKAMOOR 18th – 20th JULY 2003

On Wednesday July 16th I had an unexpected phone call from Melissa of Channel 4’s Time Team enquiring whether I would be available from the following Friday through to Sunday to help with the reconstruction of a medieval bloomery at Eastwall Farm, Oakamoor, nr Cheadle in Staffordshire. After convincing her that I had plenty of experience with furnaces (over 40 years) and was reasonably fit, I jumped at the chance of working with a bloomery.

Introduction:-
A quick look at the literature showed that Eastwall Farm (OS 4490 0350) was documented as a bloomery site around 1290. The bloomery hearths of this date used charcoal to reduce iron ore with manual bellows to produce a bloom of low carbon iron mixed with slag in the solid state. The reduction took place at about 1200oC and resulted in a liquid slag, which was run off, leaving the solid iron as a spongy mass. After this bloom had been produced a great deal of forging was required to form the wrought iron.

The bloomery process was superseded by the blast furnace in 1593 at the Old Furnace site at Oakamoor (OS 4360 0420). The blast furnace used water powered bellows to produce higher temperatures of around 1400 oC, which resulted in liquid pig iron with a much higher carbon content than the bloomery iron. The iron from the blast furnace then required further working in a chafery to produce wrought iron.

Slags from the bloomery tend to be very high in iron, making them dense and darkly coloured. The more efficient blast furnace produces slags with a lower iron content, making them less dense and lighter in colour. The bloomery process had a low capital and could be carried out as a part time activity by farmers. In contrast the blast furnace required a large capital investment, although it produced much greater quantities of iron.

Friday – Building the Furnace:-

I arrived at Eastwall Farm at about 8am and found the reconstruction team ready to start work. The team consisted of a bloomery expert and two professional blacksmiths. Later in the day we were joined by other volunteers and the film crews.

As we had to build the furnace in a single day, rather than the usual 8 weeks some short cuts were necessary. Medieval furnaces would have been entirely built from clay, but would have taken much longer to build.

The bowl of the furnace and the slag pit were first dug out of the earth as usual. The body of the furnace was then built up using refractory bricks in the hot zone and house bricks at the top, rather than using clay alone. The furnace was about 1 metre high and 350mm diameter. A brick clay was used to line the interior and consolidate the bricks.

The air inlet or tuyere was introduced at about ground level, i.e. about 300mm from the furnace base. Unfortunately we ran out of the clay at this point, so the exterior of the furnace was coated with local clay dug from behind the barn next to an out cropping coal seam. At various stages in the construction we were visited by the film crew and presenters such as Phil Harding with his rich Wessex accent, and Tony Robinson. By the end of the day we had a completed furnace and lit a fire in it to start the final drying process.

Saturday – Producing the Bloom:-

On Saturday morning we started the furnace off with wood kindling supplied by the adjacent National Trust Hawksmoor Reserve, and then followed this with mixed hardwood charcoal. The blast was supplied by an electric bouncy castle blower, except for demonstration purposes when two pairs of hand bellows were used, the design of one coming from Agricola’s classic textbook.

At the beginning of the day we had been given a stern health and safety talk at which it was stated that the furnace gases (mainly carbon monoxide) would "explode" when the furnace was hot and ready for charging with ore. When this happened it was quite spectacular, removing some of the blacksmith’s hair and eyebrows. The charge consisted of equal weights of charcoal and haematite ore. Initially the furnace was kept full with the charge gradually sinking into the hot zone of the hearth. When the charge had burnt down, slag tapping was attempted through the tapping arch into the slag pit. About 4 or 5 tappings were made although our slag was rather more viscous than we would have liked for tapping off.

The slag is produced from a mixture of siliceous materials in the ore, iron from the ore, the clay furnace lining and ash from the charcoal. As it was thought our slag was too low in silica, sand was added to the charge to help the fluxing action. The tapping hole was resealed with grass turfs cut from the surrounding field and some additional clay. Looking into the tuyere enabled the temperature of the furnace to be gauged at 1200 - 1400 oC, this melted the clay liner forming stalactites which were broken off with an iron rod.

At the end of the day when the charge had melted down almost to the level of the tuyere, attempts were made to remove the bloom. After considerable efforts by the team a rather poor bloom weighing about 5kg was extracted from the furnace.

Sunday – Forging the bloom:-

The object of the exercise on Sunday, the last day of the Time Team dig, was to forge the bloom down to a usable form of iron. Before this work started I had a look at the remains of the medieval bloomery hearth being excavated in the next field. This was very similar in shape and size to the below ground part of our reconstruction.

In order to convert the bloomery furnace into a forging hearth we removed about 400mm from the top of the furnace and relined the base with more of the local clay. The previous days firing had fully vitrified the original clay lining around the tuyere, melting it away from the brick core. Unfortunately the rough glass interior of the fired furnace resulted in a badly cut finger for the bloomery expert, and a trip to Leek Hospital.

As the team was now a little short handed (no pun intended) I had to don my safety glasses, boiler suit and sun hat, and get into action on the furnace controlling the air supply to the forging hearth. The bloom was reheated in the furnace and worked down on a wooden block with a wooden mallet to consolidate the iron and squeeze out the excessive slag content – about twenty reheats and forgings were carried out. When the bloom was deemed solid enough to be forged with an iron anvil and hammer, the process continued this way. Unfortunately the bloom developed a crack which curtailed the work on this material. A more solid bloom from a previous smelting process was then forged with multiple striking of the metal by a team of blacksmiths hammering in turn.

Conclusion:-

After three days of most interesting work, I now have a much better knowledge and understanding of the bloomery process than that gained previously from textbooks and articles. I look forward to the Time Team programme which is expected to go out early next year to get the rest of the story. It was a real eye opener to see the great effort put in over the three days of a Time Team production, producing about 24 hours of film, which is then edited down to about 45 minutes of television viewing. My sincere thanks to Channel 4’s Time Team for letting me get involved in such a unique experience.

Jim Andrews (Chairman SIAS) see also Channel 4’s Time Team web site

Our current project is helping to restore Sandon Lime Kiln, see Sandon Lime kilns

Further details from Jim Andrews 01785-246101

		Staffordshire Industrial Archaeology Society