Dear Karel,
The size and shape is typical of a smithing-hearth bottom, the
result of iron-working. I have seen examples of these that contain
both metallic copper prills and copper corrosion products. The
source of copper can be because the hearth was used for working
both ferrous and non-ferrous alloys (in the case of metallic
copper-prills), or from contamination from copper-salts leaching from
nearby non-ferrous artefacts. You can also get elevated levels of
copper in iron-working slags when high copper iron is being worked.
In general, it is best to assume that this sort of material is
the result of iron-working unless there is other evidence of copper
smelting present. Such evidence from the slag might include the
following features. The presence of copper sulphide prills in the
slag, or the presence of crushed and partially digested quartz
fragments (used to flux the iron present), or that the number of
metallic copper prills predominate over iron.
On Tue, 4 Apr 2000 09:56:28 +0000 [log in to unmask] wrote:
> I´m examining archaeometallurgical finds from one of preurban sites
> in Prague area (12th - 13th century). There is nothing special there
> except of several very small slag cakes with oval ground plan,
> planconvex profile and dimensions cca 7 x 5,5 x 2 cm. Their upper
> surface shows typical flow texture, the bottom one is covered by
> sandy crust. By the chemical and phase composition it might be a
> typical copper smelting slag with fayalit in glass matrix
> (FeO share around 30%) and rare inclusions of secondary
> Cu minerals. I still cannot imagine the corresponding type of
> production and furnace: it could be some miniature smelting or
> refining shaft furnace with a taphole. Can anyone help me to find an
> adequate interpretation of these objects?
>
> Thanks
> Karel Novacek
> Dept. of Archaeology, University of West Bohemia Pilsen
Chris Salter
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