Ingo-
I am interested in your announcement of standard ESK-1, particularly as
you note that the slag contains metallic iron. I am curious to know how
you achieve even dispersion of the metallic iron in the powdered reference
sample. I'm not sure how many people on this list know what is involved in
the certification of an international geochemical reference standard, so
(for those who do) forgive me for noting that the first and most critical
step is the preparation of a homogeneous powder from a sufficient
quantity of the chosen material. The amount of material that must be
homogenized depends upon anticipated demand for the standard; for the
hematite ore standard SARM-11, for example, 400 kg of the ore were
ground and mixed in an elaborate multi-stage procedure to produce 3700
bottles of standard, ground such that 90% passed a 400 mesh screen (Stoch
1978).
Obviously an archaeometallurgical standard need not be prepared from such
a large amount, but the necessity for homogeneity is the same. To prepare
a fine powder, the samples must be ground. My past experience with the
grinding of slags containing metallic phases (whether copper, lead or
iron) is thatone can't disperse the metal evenly. In fact, the reverse
occurs - metal aggregates into small prills, or gets smeared onto the
surface of the grinding media. This is hardly suprising, as this is
exactly the mechanism by which gold nuggets form in stream beds from
agglomeration of dispersed grains, but it makes it virtually impossible to
achieve a homogenous dispersion of the metallic phases in slag powders.
I have never really solved this problem, and would be interested to know
how others deal with it.
Reference cited:
Stoch, L. (1978) The Preparation and Certification of a Reference Sample
of Hematite Ore. Randburg (South Africa): National Institute for
Metallurgy, Report no. 1977.
----------------------
David Killick
Associate Professor, Department of Anthropology,
University of Arizona, Tucson, AZ 85721-0030.
Phones: office (520)621-8685; laboratory 621-7986; fax 621-2088
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