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Quote:Even though there's 34x more zinc than tin available? If the amounts were closer I could see ease of refinement and such being relevant, but I'd have thought that sheer lack of abundance in relation would make tin more costly regardless of it being less-easy to make brass by cementation...
Reading the Wikipedia article on Zinc had some clues about zinc production in ancient times. http://en.wikipedia.org/wiki/Zinc I suspect that the types of Zinc ores that were usable then were less abundant than tin. I have read elsewhere that in the Roman Empire brass was generally reserved for coinage and military use. Anyone remember any ancient writers
discussing brass and it's manufacture? Here is an interesting article on Roman brass coins. https://kb.osu.edu/dspace/bitstream/181 ... 03_137.pdf
This document suggest that Zinc sources were declining in the Roman empire based on analysis of Roman brass coin chemical composition:
https://kb.osu.edu/dspace/bitstream/181 ... 03_151.pdf
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Quote:Matt Lukes:3tse78qq Wrote:Even though there's 34x more zinc than tin available? If the amounts were closer I could see ease of refinement and such being relevant, but I'd have thought that sheer lack of abundance in relation would make tin more costly regardless of it being less-easy to make brass by cementation...
Reading the Wikipedia article on Zinc had some clues about zinc production in ancient times. http://en.wikipedia.org/wiki/Zinc I suspect that the types of Zinc ores that were usable then were less abundant than tin. I have read elsewhere that in the Roman Empire brass was generally reserved for coinage and military use. Anyone remember any ancient writers
discussing brass and it's manufacture? Here is an interesting article on Roman brass coins. https://kb.osu.edu/dspace/bitstream/181 ... 03_137.pdf
This document suggest that Zinc sources were declining in the Roman empire based on analysis of Roman brass coin chemical composition:
https://kb.osu.edu/dspace/bitstream/181 ... 03_151.pdf
Perhaps segmentatas whet out of use in the late empire partly because brass for fittings became more expensive nad hard to get!
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Dr. Thomas,
I have been having a hard time finding the pitch bark and bitumen here in NY. I have done some searching and it is not easy to come by. Maybe, I have not searched enough.
I was entertaining the idea of molasses, tar, and lard since they are the most similar and available.
"You have to laugh at life or else what are you going to laugh at?" (Joseph Rosen)
Paolo
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The confusion seems to be difference between the abundance in the Earth's crust and where you actually find the stuff. The zinc ores tend to occur concentrated, whereas the tin are more diffuse, despite being 'more abundant'.
Caratacus
(Dr Mike Thomas)
visne scire quod credam? credo orbes volantes exstare.
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Quote:The Roman method of production was called the cementation process. It was a batch method and probably failed as many times as it worked as it depended on fairly precise temperature control - which was presumably achieved through looking at the colour of the pot in which the reaction was taking place (in the same way that a blacksmith judges the temperature of the iron from the colour of the hot metal).
David Sim is about to begin a series of experiments at Butser to actually do this - turns out nobody has (it is all just theory, folks!). He asked around amongst everybody who has written about it and it seems nobody living seems to have made brass by the cementation process the way the Romans would have done. So he is going to. Oh, that and molten iron too ;-) ) He wants this publicised, so once he has built his kilns and has some dates, I will pass them on, in case anybody wants to go down and join in.
Incidentally, he and Jaime Kaminski have a book on the manufacture, testing, and analysis of Roman armour in preparation and, having read a draft of it (and please excuse the pun), it is hot stuff... and nary a leather seggie in sight!
Mike Bishop
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Quote:Just to add a few facts: 
founding dates of important historic journals:
1859 Historische Zeitschrift
1876 Revue Historique
1884 Rivista Storica Italiana
1886 English Historical Review
1895 American Historical Review
Off topic, but I couldn't let this one go by ... 
1851 Proceedings of the Society of Antiquaries of Scotland (with a report of a couple of nice Roman altars found at Newstead) !!
Now ... back to (what was it?) bronze segmentata ...
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But isn´t that rather on material culture than on history / historiography? Cool, anyway!
Christian K.
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Quote:David Sim is about to begin a series of experiments at Butser to actually do this - turns out nobody has (it is all just theory, folks!).
Mike B:
Good Oh! I've seen a reference somewhere in an American journal to the cementation prcess (American Journal of Experimental Archaeology, perhaps?) to the process, but I don't think they actually tried it. I'd be very interested to see what David Sim makes of this - the chemistry is quite complicated and there is no way that a Roman foundry smith could have worked it out - other than by a process of 'trial-and-error'. Unless, of course, the Romans knew an awful lot more about phase diagrams than we have hitherto given them credit for .....
On another matter - progress is being made and I shall be in touch in a few weeks (maybe less).
Caratacus
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Slighty related to "funny chemistry": Near the city where I live, the prerroman people developed a extremely complex sistem to embellish the weapons ("Monte Bernorios" and related stuff):
![[Image: presento2+049.jpg]](http://bp1.blogger.com/_nUHJZ3u-SG8/SD7YZ3zOSvI/AAAAAAAAAEc/-nB9l5r8iXo/s400/presento2+049.jpg)
![[Image: presento2-4071.jpg?w=300]](http://armasmagnetita.files.wordpress.com/2008/06/presento2-4071.jpg?w=300)
![[Image: pomodch.jpg?w=300]](http://armasmagnetita.files.wordpress.com/2008/06/pomodch.jpg?w=300)
You had a nucleus of iron, then put over some bronze leafs with high content in tin, and over this another one of iron. Then, after a thermic treatment (without melting the bronze), you have a nice magnetite surface to embellish with silver wire.
The curious thing it's that the superficial magnetite can be archived without that complex bronze inner covering, and they did with and without it. Even some Medieval stuff has this magnetite finish.
There is a nice blog (mostly Spanish), carried by one of the members of the research team (Quesada/ Thersites is also in) devoted to this technique:
[url:12zeiwzw]http://armasmagnetita.wordpress.com/[/url]
-This new learning amazes me, Sir Bedevere. Explain again how
sheep´s bladders may be employed to prevent earthquakes.
![[Image: escudocopia.jpg]](http://i214.photobucket.com/albums/cc320/iagoba_f/escudocopia.jpg) Iagoba Ferreira Benito, member of Cohors Prima Gallica
and current Medieval Martial Arts teacher of Comilitium Sacrae Ensis, fencing club.
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Quote:On another matter - progress is being made and I shall be in touch in a few weeks (maybe less).
Excellent - our plan for world domination moves one step closer (MUAHAHAHA)!
Mike Bishop
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Quote:Excellent - our plan for world domination moves one step closer (MUAHAHAHA)!
Ssshhhhh! There are people out there in GCHQ who read this stuff!
Caratacus
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Quote:The confusion seems to be difference between the abundance in the Earth's crust and where you actually find the stuff. The zinc ores tend to occur concentrated, whereas the tin are more diffuse, despite being 'more abundant'.
Caratacus
(Dr Mike Thomas)
It's the other way around- general abundance of tin is far less than that of zinc; and if tin or is more diffuse whereas zinc is concentrated, that'd fit with bronze being more valuable just as it is today- or do you mean that the other way around as well? Certainly concentration and access are important and I'd have thought them more relevant if the abundance ratio weren't as high 34:1 (Zn:Sn).
See FABRICA ROMANORVM Recreations in the Marketplace for custom helmets, armour, swords and more!
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Quote:It's the other way around- general abundance of tin is far less than that of zinc; and if tin or is more diffuse whereas zinc is concentrated, that'd fit with bronze being more valuable just as it is today- or do you mean that the other way around ?
B*gg*r! You're right. Teach me to read a post more carefully before replying. I put that very badly and confusedly. (In my defence, I was trying to carry out a phone conversation at the same time as typing the post - clearly multi-tasking is beyond me these days!) Let me try again, in more detail and with more thought. I should stress that this is just speculation on my part!
The two main ores of zinc are Zinc Blende (zinc sulphide, ZnS) and Calamine (Zinc carbonate, ZnCO3 - sorry, can't do subscripts here). Because of the complex chemistry involved, I doubt that 'the ancients' could cope with Blende to extract zinc - it certainly would not work in the cementation process, unless the ore was pre-roasted to convert to the oxide. Zinc carbonate (calamine), however, would decompose under the conditions for the process inside the pot and so would not present this problem. Now, I don't know what the relative abundance of these two ores is, but I suspect that calamine is far less common than blende - and that may be the source of the problem here. There is also a sulphate ore of zinc, but this would be of no use as it is extremely stable and requires a very high temperature to decompose it to the oxide.
So far as I know, the only common ore of tin is cassiterite (the oxide), which in Britain at least only really occurs in the Cornish peninsular in sufficient quantities to be worth while extracting. However, the ores here are quite rich. Until recently there was even a working tin mine there (Wheal Jane, I think it was called). There are dozens of old tin mines in the county, some of them certainly stretching back to Roman use. There are also tin mines (no longer used, but also going back in at least one case to Roman times) in North Wales. However, I have never heard of anywhere in Britain where the Romans extracted zinc ores
What it boils down to is that the crustal ratio of zinc to tin may not matter very much - the way in which the two metals occur may be of a much higher relevance. If 95% of the zinc ores cannot be used (because they are Blende) and ALL the tin ore can be employed, then this brings the two metals much more into alignment. I think! :wink: Does that make sense?
Caratacus
(Mike T)
visne scire quod credam? credo orbes volantes exstare.
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