VSF 2010 Report - Nabo

which the fragment originates. A small fragment had a smooth curved inner surface, with the
impression of some sort of channel no more than 2cm in diameter, context [6057]. The inner
surface is smooth due to heavy vitrification, and may bear the cellular impression of a wooden
fragment such as a branch. This technical vitrification may be the impression of an air hole or
a tapping hole through the furnace wall.
Several other smaller fragments of technical vitrifications were identified. Their size,
unfortunately, does not allow for any estimate of the size or shape of the larger parent body. It
is possible that some of the fragments may relate to a hearth. However, the contextual
evidence suggests that these fragments are related to a furnace construction used for smelting,
due to the concurrence of technical vitrifications with contexts abundant in iron production
residues.
Ferruginous concretions
Iron rich concretions appear frequently throughout the assemblage. The contexts with the
highest concentration of ferruginous concretions correspond with those contexts prevalent in
iron production residues. In particular, the largest concentrations are contexts [319], [6057]
and [7012], which also bear considerable quantities of smelting slags. The other contexts
containing notable amounts of ferruginous concretions are [204=251=302], [318], [324] and
[332]. Some concretions were identified as nails and excluded from this assessment. Most of
the ferrugionous concretions displayed colours common to iron corrosion products, such as
reddish and yellowish iron oxides and purplish iron hydroxides. These need not be restricted
to metallic objects. Although it is likely that some of the ferruginous concretions represent
metallic bodies that have completely corroded, many of the lumps identified have a close
resemblance to reduced pieces of ore. Further analysis is needed to confirm the nature of the
iron rich concretions in order to better establish whether they represent discarded/unused iron
ore.
Other
Most of the other residues identified within the assemblage were stones. One type of material
that may be worthy of further investigation is the burnt bone that was found within two
deposits, [6069] and [6096]. Although burnt bone is not uncommon to many archaeological
sites, there is a possibility that it may be related to ferrous metallurgy as it has been
demonstrated in other contemporaneous sites in Scandinavia that it was used as a fuel for
smithing (Gansum 2004). If this were the case, the material should be more prevalent,
however, the fragments recovered here represent those incorporated with the slag in sampling
bags and not the reality of any on-site deposit.
Special finds
In context [7059], ten unrefined iron blooms were recovered. The deposit represents some
44kg of unused iron. The description of each unrefined bloom can be found in Table 4 and
seen in Figure 20. Although the weight of each bloom varies between 3 and 5.5kg, they show
a strong degree of similarity in terms of their dimensions, shape and form. Two forms appear
to exist: a plano-convex bloom and a flattish-oval bloom. Although there is some variation in
the diameter, they largely appear to be around 18cm across. They are not all perfectly circular,
but tend to be more oval shaped.
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