Brass analysis

APB to all historical metallurgists:

I am working on an enormous project examining and analyzing some 90
ancient brasses from West Africa, most of them never seen outside of
Nigeria and am discovering some very unusual and fascinating alloy
compositions. Of interest is the discovery of two objects with
identical spectra which are zinc alloys, that is, they have at least
twice as much zinc as copper in the alloy.

The pieces are well-provenenced and only one has shown itself to be
a forgery.  My question is: has anyone ever heard of a zinc alloy
used in antiquity, (ie, before 1000 A.D.?  West Africa is loaded with
zinc mines, and no doubt the brasses were made from smelting the
ores from rocks that contained both zinc and copper ores.  Copper
mines are far less prevalent in the area as zinc mines.

I've also analyzed a very unique (and very old) brass "double bell"
which contains a significant amount of Mn, unusual for this area,
though Gabon has many Mn mines in use today.  I'm thinking that this
object may be an "import," and if so, has anyone heard tell of an
ancient brass with significant manganese content?

Susan White
White Conservation Services


                                  ***
                  Conservation DistList Instance 25:8
                   Distributed: Monday, July 25, 2011
                        Message Id: cdl-25-8-023
                                  ***