Without wishing to divert too far from the main topic (mining of manganese
ores for decolouring glass or smelting (?iron)). John brings up the
frequently heard claim that manganese was used in the distant past for
smelting iron. I've heard this often before, but without any sound evidence.
Are these assumptions based on the more recent past?
In modern alloys, manganese may be present within steel in sufficient
quantities to enhance its properties. In historical and recent iron/steel,
where fossil fuels were used, manganese will usefully combine with the
detrimental element sulphur to form harmless manganese sulphide inclusions.
In the nineteenth was also found very advatageous to use high manganese cast
iron when puddling (a decarburising process) steel and similar processes may
have found this in the preceeding 2 or 3 centuries.
Back beyond this I know of no good analytical or archaeological evidence for
deliberate addition of manganese (or co-smelting of the ore). In fact in the
charcoal-fuelled bloomery furnaces, used from the iron Age until the late
medieval period, smelting temperatures would be too low to reduce more than
trace levels of manganese from the ore into the metal.
Looking at steel used for armour, I did find a distinct rise in the
concentration of manganese in South German steel in the sixteenth century.
However, I believe this is associated with the use of a more recent
development the more highly reducing high bloomery (stuckofen) furnace. Even
so the mean content of manganese reached only 0.04%.
Gerry McDonnell used to point out one possible advantage of high manganese
iron ores - although they pass into the slag during smelting, in doing so
they remove some of the gangue (unwanted rock), thus slightly improving the
yield of iron. However, there would be no advanage in separately mining
manganese ores to add to the iron ore.
A few thoughts
David Starley PhD
Science Officer
Royal Armouries
Armouries Drive
Leeds, W. Yorks
LS10 1LT
UK
tel 44 (0)133 220 1919
fax 44 (0)133 220 1917
-----Original Message-----
From: John Colby [mailto:[log in to unmask]]
Sent: Sunday, October 17, 1999 5:56 AM
To: [log in to unmask]
Cc: [log in to unmask]
Subject: Re: Manganese etc.
------------
In making glass, the addition of Mn would make the glass very brittle.
The main mineral used for colouring glass is cobalt. Evidence is around
from way back in the iron age that Mn was used in the smelting of iron
ore. The Mn ore was smelted with the iron ore and the resulting mixture
used to make tools. These early people soon found out that the dual
smelt produced a metal that kept its edge for longer.
The mining of pyrolusite and rodochrosite would not have been the main
source of the Mn. These minerals are rare and it would be more common to
find wad (Co-Mn complex). R'site was used and still is used as a gem
stone (a pink colour). Jewellery has been found which has used R'site in
a crude polished form from Roman and contemporary sources.
------------
The original query response series was down to a mining history question
on Roman use for manganese other than as semi-precious stone - which,
Anne, prompted my extension about whether any minor and trace element
analyses had been performed on mineral manufactured artefacts. Earlier
in the above correspondence I had referred to Adkins handbook which gave
Mn as the source for glass colourant.
In the Cornubian province the exploitable reserve of manganese is much
less widespread than iron - at least according to historical mining
records rather than chemical analysis. I suppose the next step (for me)
is to map the minerals found per mine onto my existing minerals mined
from records maps to see if there is any correlation.
Regards
John
--
John Colby
Website at http://www.colbybos.demon.co.uk
Last Updated Sunday 10th October 1999
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