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There are two persistent metallographic characteristics
in just about all of the 151 samples of both
the oxhide and bun-shaped copper ingots. One is the
constant porosity, some large and some small, generally
present in all the samples studied so far. The
other is the ubiquitous presence of different phases
and compounds inside the copper matrix.

Porous Volume of the Copper Ingots. Throughout
the samples we observed the porous volume
typical for "blister copper." The ingots contain numerous
cavities that can be classified in sizes of a
few micrometers up to several millimeters. It can be
demonstrated by the plugs drilled from the ingots
that copper oxhide and bun-shaped ingots of the
Late Bronze Age have an enormous porous volume
that exceeds by far our previous ideas on their inner
structure (figs. 1-5). The volume locally reaches
up to 20% or even higher. In general, cavities like
these are caused by the effervescence of gases such
as oxygen, carbon monoxide, and carbon dioxide, by
water from burning charcoal, as well as by sulfur
dioxide from oxidation of sulfide inclusions in the
copper in the liquid state. The gases dissolve violently
during solidification, a phenomenon known in
metallurgy as "Spratzen." In addition, porous volume
is caused all over the ingots by interdendritic
shrinkage (fig. 6). The porosity is high in the upper
part of the ingots. Near the bottom, the porous volume
is low, the structure is more dense and hence
much less affected by corrosion over the millennia.
The distribution of the porous volume, in addition,
is irregular. This is exemplified in the oxhide ingot
KW 1548/7b, where parts of dense copper alternate
with those high in bubbles and cavities (fig. 2) and
are sharply separated from each other. This could
be caused by pouring several batches of metal into
the mold to complete an ingot, an observation supported
by macroscopic evidence (Pulak 2000: 142,
fig. 6).
As shown by previous studies (see above), the
high porosity seems to be a characteristic feature of
Late Bronze Age copper ingots with a provenance
from Cyprus

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The third type of inclusion
is made up of nearly pure copper sulfides as
observed already in the slag inclusions. They form
droplets aligned along the grain boundaries of copper,
very similar to the cuprite inclusions. These are
relics of the sulfidic ore used for smelting. This
seems to have been a well-developed technology at
Late Bronze Age Cyprus.