VSF 2010 Report - Nabo

Non-diagnostic residues
The terms ‘smithing slag lumps’ and ‘cinder’ are utilised as terms in some classification
systems. These two definitions are not used to classify the residues in this investigation.
McDonnell and Maclean describe work on the premise that all slag should be described as
smithing slag “unless there is good evidence to indicate that it derived from the smelting
process” (2010: 272). They describe such “smithing slag lumps” as “randomly shaped pieces
of iron silicate slag generated by the smithing process” (ibid.). It may appear logical to
assume that slag is smithing slag until proven to originate from smelting, but this assertion
can be misleading. An assemblage of highly fragmented and altered smelting slag lumps may
appear non-diagnostic and, working within McDonnell and Maclean’s terminology and
classification system, would be misconstrued as ‘smithing slag’. Whilst smithing slag
produced in a hearth can comprise randomly shaped lumps, they cannot necessarily be
distinguished from other slag types. To avoid any misidentification, this report does not adopt
the term or classification of ‘smithing slag lumps’. Such slag lumps, exhibiting no clear
features indicative of a particular process, will be deemed undiagnostic. This does not mean to
negate the term ‘smithing slag lumps’ altogether. Contextual evidence can significantly
increase a confident identification of slag lumps generated by smithing, such as when they are
found in-situ in a hearth.
‘Cinder’ has appropriated several different meanings during its usage and is imbued
with ambiguity. Burnt or part-burnt material that has sintered (not melted) together to form
lumps may be called cinder. The term is not exclusive to metallurgy. It can be used loosely to
refer to material deriving from pyrotechnical processes generally. In metallurgy, it may refer
to agglomerated material that floats above molten metal or slag. Historically, the term
generally meant ‘slag’ (though no always). ‘Cinder’ has also been used as a term to refer to
coke, or a coke oven (Neilson 1842: 17). McDonnell and Maclean defined cinder as “high
silica-content slag that forms between silica and ferruginous material... [which] may include
pieces of lava” (2010: 273). Equally broad definitions have been used in other categorisation
systems to include ‘fused earth’ and ‘siliceous-slag’. The breadth and ambiguity of the term
cinder prevents it from being used in this report. Slag that would be identified as ‘cinder’ is
likely to be identified as either ‘undiagnostic slag’, or ‘fuel ash slag’.
Undiagnostic slag
Slag lacking diagnostic features often is often difficult to assign to a particular process, i.e.
smelting or smithing. ‘Undiagnostic slag’, as it has come to be termed, can form significant
portions, if not the majority, of slag assemblages. Undiagnostic slag often consists of small or
fractured pieces of slag, sometimes corroded. As larger diagnostic slag entities undergo
various post-depositional processes, they inevitably fragment into smaller pieces, depreciating
in diagnostic features. Despite the difficulty of identifying a particular process, it can be
assumed that some form of iron-working is taking place. Some undiagnostic slag fragments
may exhibit intermediate characteristics of specific slag types, hinting at a process without
full certainty.
Flowed Slag
During the assessment of the residues from Vatnsfjörður, an category of undiagnostic slag
was identified, closely matching the description provided by McDonnell and Maclean (2010:
273). This slag exhibits no diagnostic features indicative of any particular process. However,
different to undiagnostic slag proper, this slag does display different morphological features.
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