VSF 2010 Report - Nabo

providing some information about the smelting environment. The flattish stones are likely to
form part of the furnace architecture. The smaller stones may also define the lower
subterranean limits of the furnace.
Smithing Hearth Bottoms
The recovery of smithing hearth bottoms/fragments and hammerscale indicates that the
activity was taking place on site. Of the 29 fragments recovered, nearly half of them derive
from context [319]. Notable concentrations of SHB’s also occur in context [204=251=302],
[6057] and [6096]. Despite having the most fragments, context [319] is exceeded by context
[6057] in weight, due to the fact the SHB’s are large and mostly complete. The more
complete fragments indicate that they were roughly 10-11cm in diameter, although there is
some variation in size. They all show a degree of curvature and roughness to the under
surface, the bottom, generally with a flattish or slightly concave upper surface. Some
examples of smithing hearth bottoms can be seen in Figure 8. Some of the smithing hearth
bottoms have a relatively smooth upper surface, which may owe its presence to high smithing
temperatures allowing for some liquation of the slag. This would also explain the abundance
of flowed slag, which display the flowed characteristics induced by high smithing
temperatures (however, not all flowed slag necessarily relates to smithing). The smithing
hearth bottoms do vary in appearance slightly. Those from context [6057] have a reddish
luster with a rust type residue, probably incorporation of smithing residues rich in iron. Alone,
the smithing hearth bottoms are not indicative of primary or secondary smithing, as this
interpretation relies heavily on the presence/absence of smelting residues and spheroidal
hammerscale.
Hammerscale
Magnetic residues were collected from almost every context examined. Whilst these residues
are informative of smithing, not all magnetic residues are necessarily hammerscale. The
difficulty in separating hammerscale from other magnetic material is difficult. In contect with
the other archaeometallurgical residues, the magnetic residues collected here are probably
hammerscale, which can be microscopic. The contexts most abundant in magnetic material
are [204=251=302], [319] and [6057], which corresponds well with the recovery of smithing
hearth bottoms/fragments. Over 230 slag spheres were recovered from the sampling bags.
Almost all of these derive from context [6057]. Although this sample does not reflect the real
extent and number from the site, their presence is informative of the type of smithing that was
taking place. Whilst secondary smithing (repair, rework, manufacture) is a common activity,
bloom refining (primary smithing) is not. The evidence for iron production yielded from the
slag assemblage, in conjunction with the spheroidal hammerscale recovered from the
sampling bags, demonstrates that primary smithing took place.
Undiagnostic slag
The majority of the slag assemblage examined was either too small to identify, and/or the
fragments exhibited no diagnostic features. However, when taking into account the diagnostic
residues examined, the nature of the diagnostic slag may imply a particular process. Contexts
[204], [319] and [324] are all strongly indicative of iron production due to their quantities of
smelting slag and tap slag. These contexts also show an abundance of flowed slag. The
undiagnostic slag are larger than the undiagnostic residues of other contexts, which may
indicate that these undiagnostic and flowed slag lumps are fragmentary iron production slags.
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