|A practical experiment in the use of local materials in the iron smelting process
Whitehall farm, Nether Heyford 2001
It is the aim of this project to produce a workable bloom from local materials as authentically as possible.
The making of iron using an early furnace is acknowledged to be difficult. This experiment attempts to recreate the process with the additional handicap of using only locally obtained resources. The charcoal will be the only possible exception, it being sourced from a supplier 12 miles away, all other materials will be obtained from Whitehall farm.
Evidence of iron working has been found at Heyford Villa during excavations carried out in 2000-01. This has taken the form of a bloom and several substantial pieces of bloomery slag spread in a stratographic sequence suggesting a date no later than 300CE.
Evidence of early ironworking in Northamptonshire has been documented at Laxton, Wakerley and Bulwick (Jackson and Tylecote Britannia [198?]).
Although ironmaking continued up to the end of the Roman period it was not revived in Northamptonshire until 1850, the first furnace also being sited in Nether Heyford: Griffith's guide of 1873 reports:
"Northampton during the last fifteen years has become an important
This experiment is the first part of an ongoing paper that will seek to explain why this gap of 1400 years occurred, hence the reliance on local materials. It will also give a clearer idea of the problems encountered in the process. It is worth noting that prior to the writer's degree he was involved in most practical aspects of iron and steel production and the working of the finished product.
Ironstone was collected from the surface during the course of the excavation at Whitehall farm July 2001. It was broken into pieces of no more than 25mm and washed to remove all Jurassic sand deposits. Evidence of calcined ore has been found at Heyford (2001 Report to follow). Due to the quality of the ore it was decided to calculate the ore. This consisted of digging a pit 600mm x 900mm x 300mm deep. A charcoal fire was lit, the ore placed on top and covered in turf and soil to provide a semi airtight seal. This process was unsuccessful as the ore was only partially calcined. A second attempt did not cover the ore with soil and was a complete success, the ore turned a deep red and became very brittle.
Charcoal was obtained from sustainable managed forest and mainly consisted of hazel lump-wood. The pieces were broken into pieces of less than 100mm. The smaller pieces and dust were collected for the initial firing of the kiln.
The tuyeres were produced from local clay and were a rough trapezoid measuring 610mm long, 100mm outer dia at flange and 50mm dia at outlet; the wall thickness throughout was 20mm. The tuyere/s were placed in the furnace's inlet aperture and sealed with clay.
The weather, week commencing 16.7.01 was extremely wet and did not allow the furnace to dry sufficiently! Therefore the only firing possible was on Sunday 22.7.01 (the open day and fund raising of an ongoing Roman villa excavation). No pyrometer was available so it was decided to watch the flame for an indication of temperature. The tuyeres were placed at a 90-degree angle and centred in the furnace, they were then fixed in place with clay. The slag hole was filled with a stone and likewise stopped up with clay. A wood fire was lit and charcoal placed on top. Due to the wet condition of the furnace this was allowed to sit for 30 minuets before blowing.
5Kg of iron was produced from this experiment, however not in conventional bloom form. There were several restrictions placed which could have effected the outcome:
I The furnace was wet at the initial firing, indeed the outside was still wet after the experiment which only continued to give open day visitors a display, the experiment per se was written off at 7.00 am when the first cracks appeared inside the furnace.
2 The visitors (whilst accepted as our reason for being there) proved to be a serious health and safety risk and therefore it was decided to keep the furnace partially covered for most of the duration of the melt, therefore obscuring the colour of the flame except when removed.
3 The lack of pyrometer proved to be a mixed blessing: the feel of the metal was enhanced, but there was no way of monitoring the temperature as an ongoing factor.
4 The bellows, while primitive were very effective.
5 We did produce iron on our first attempt despite all these handicaps therefore proving the thesis that iron can be made from materials found locally
There will be a second attempt, the following actions will take place: