"I. Keesmann" wrote:
> I think they have and I hope that fun and science are not factors excluding
> eachother. Despite the fact that the details of the experimental reduction
> process may not be directly comparable to archaeologically well described cases
> (how few do we have and which experiment is really identical with which method
> of the ancient metallurgists ?).
> At least it has something to do with archaeometallurgy : The observations
> about the distribution of differently carburized metal relativ to its position
> to the tuyere and the behaviour of iron sponge with variable contents of slag
> during heating and hammering are most interesting, as well as the fact that
> some sort of "analysing" can be done by "only" carefully observing the
> behaviour of materials during processing them.
Well said. I thought that some of the earlier comments on the Rockridge bloomery
were unduly harsh. Remember that their perspective is that of the blacksmith; their
original motive for smelting was to produce some real wrought iron for the forge.
As other contributors to this list (e.g. David Harvey) have noted, wrought iron is
a very different material in the forge than the mild steel that modern blacksmiths
have to work with. The interest group here is the artist blacksmith community, not
archaeometallurgists.
>> The role of preheated air has been discussed concerning African smelting
>> processes and may perhaps be one of the essentials of the Matacam process
>> (David KILLICK ?).
>>
Not as far as I know. The idea that the long vertical tuyere (1.5 meter) that is
characteristic of iron smelting in north Cameroon may have provided preheating
originated with Tylecote ("Iron smelting in pre-industrial communities", Journal of
the Iron and Steel Institute 203:340-348). See p. 345, where he says the following:
"This arrangement probably ensures considerable preheat, though calculations based
on simplifications such as very small surfaces show that this is almost
negligible.If small pebbles were placed inside this tuyere the heat transfer
characteristics would be much improved" This is a pretty confused analysis. The
calculations that he refers to can only be for laminar, one-way, fluid flow through
a smooth pipe. In fact the bellows used in the process are valveless, so flow in
the pipe is certainly turbulent and the residence time in the tuyere considerably
increased over one-way flow. These characteristics ought in theory to assist
preheating of the air, but I found no evidence for this when Nic David and I
recorded a succesful smelt in one such furnace in Cameroon in 1989. The maxiumum
temperature that I measured with a Pt/Rh thermocouple below the mouth of the tuyere
was only 1380C.
I have argued against claims for preheating in hand-powered bloomery furnaces, as
has Ned Rehder - for our criticisms, and responses by Peter Schmidt and Don Avery,
see Peter Schmidt (ed) The Culture and Technology of African Iron Production
(University Press of Florida, 1996). The only bloomery furnaces that have been
proven to have used preheated blast were the water-powered furnaces of the American
bloomery process in the 19th century, where the incoming air was forced through
cast iron pipes embedded in tall brick chimneys above the bloomery hearth (see
Gordon, Robert B. and David Killick,"The metallurgy of the American bloomery
process", Archeomaterials 6:141-167 (1992)).
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