An Archaeology of Trafford in 12 Objects Part 7: Medieval Iron Furnace Slag

The seventh piece in our festive look at the archaeology of Trafford in 12 objects, is a large chunk of iron slag that formed the base of a medieval furnace. This was roughly 550mm across, 300mm wide and over 200mmm deep, the outer edge of the slag preserving the bowl-shaped base of the iron furnace.

This hefty item was discovered during a dig undertaken by the University of Manchester Archaeological Unit between May and July 2003 on the Trafford/Manchester border along Whitecarr Lane in Hale Barns. An area 10m by 15m was dug ahead of the laying of water pipe for United Utilities. The discoveries included a roasting hearth as well as the fragments of a late medieval bloomery iron furnace. The excavated portion of the iron working site lies within Manchester, but the unexcavated majority of the site is sited within Trafford, hence its inclusion in this list.

A total of 50.62 kg (approximately 990 fragments) of industrial waste from Whitecarr Lane was recovered. Most of this assemblage (25.25 kg, 657 pieces) consisted of heavily broken fragments of non-diagnostic slag with a highly vesicular structure. The next largest proportion of the assemblage was composed of tap slag (18.60 kg, 247 fragments). 39.05 kg (624 fragments) came from contexts within the iron furnace, although some slag was recovered from a second pit to the south of the furnace. The weight of the bowl-shaped iron furnace, and the fact that the water pipe would not damage this part of the site, led to the decision to leave most of the heavy furnace remains in the ground.

The industrial waste from Whitecarr Lane is typical of the products of the bloomery furnace commonly in use for the smelting of iron in Britain from the Iron Age to the sixteenth century. However, fragments of slag fused to green-glazed pottery suggested an end date for the furnace’s operation in the fourteenth or fifteenth centuries. It is one of seven late medieval bloomery sites known from Greater Manchester: the Castleshaw Valley at Cudworth Pasture and Spa Clough; Chorlton Fold in Salford; Cinder Hill in Farnworth; Gadbury Fold in Leigh; snf Holcombe Moor near Ramsbottom.

It’s not clear where the iron ore came from that was used in the Whitecarr Lane bloomery site, although the suspicion is that it must have come from the local geology close to the site or even from local bogs (bog iron). The charcoal fuel for the furnace would most likely have been manufactured locally from managed woodland. It’s even possible that the iron from this site was used to make some of the iron objects such as the nails and adze found at Timperley Old Hall, just a few kilometres to the west.

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