Thanks very much to Tobias Skowronek for
replying to my earlier query about chemical and lead
isotopic data for metals in Portuguese and other
shipwrecks. I highly recommend his PhD thesis (2021) on
this topic.
I have a related query. There is a rich
cemetery in the Zambezi valley – on the border between
Zambia and Zimbabwe – called Ingombe Ilede, excavated in
1960 and 1961, and published in 1969 by Brain Fagan. The
graves contain ivory, gold, X-shaped copper ingots, lots of
Indian glass beads, cloth (preserved by contact with the
copper), iron wire-drawing plates, and lots of copper and
bronze wire in various gauges. The older radiocarbon dates
are a mess, but two new dates on cloth both calibrate (using
the SHCAL 20 curve) to the interval 1470 to 1640 AD at 95%
probability. Prior to 1531, when the Portuguese founded
their first trading post in the Zambezi valley, all imports
from outside the continent were from India, China and the
Islamic world, carried into the African interior by Swahili
merchants from their ports in present Kenya and Tanzania.
Thereafter, imports could be from these sources, or could be
European.
We are trying to decide whether the
cemetery at Ingombe Ilede falls before or after 1531. Jay
Stephens has done lead isotopes and chemistry on 15 pieces.
Two copper crosses are from the Kipushi mine in Katanga,
about 500 km away, but the non-radiogenic lead isotope
ratios obtained for the bronze wire are difficult to
interpret, being compatible with Africa, European, Near
Eastern and Indian sources. Close inspection of the coarsest
bronze wire has however convinced me that it was rolled, not
drawn. It has absolutely regular square section, about 3.5
mm on a side, and is in lengths up to 1.3 m.
What can the Arch-Metals hive mind tell
me about the early history of rolling metals in Europe? (I
have not yet found any mention of the rolling of metals in
the Islamic world, India or China before 1800). My
searching to date has turned up the 1480 conceptual sketch
by Leonardo da Vinci of a machine for rolling lead cames for
windows, but no evidence for the actual use of a rolling
mill until the 1590’s, and that for rolling and splitting
iron plate. Do you know of any evidence for the rolling of
copper rod or wire before the latter date?
