Brass / Bronze

[Andy]

What is the view of the use of brass or bronze in the reproduction of "bronze" items? I thought brass was the "poor re-enactors" substitute while bronze was the premium choice.
I have just read that Roman age bronze was more closer to that of our modern day brass. Is it more accurate to have "bronze" items made out of brass?

[LUCIUS ALFENUS AVITIANUS]

If you see some roman items with an extraordinary degree of preservation, that even have the original colour, you can see often a yellowish/golden colour. That's closer to our today's brasses than to our today's bronzes, that are more "red" or "copper" coloured.

Roman uses a lot of copper alloys. Sometimes, they have a lot of items for reciclyng, so the final result often was a alloy with a lot of components.

And for some purposes, they add some metals to the alloys. Lead, silver, etc were added to the alloy. That metals were added to change aspects as the viscosity, point of melting, hardness, colour, etc.

[Medicus matt]

Depends on what you mean by bronze and brass. Modern metallurgy have very precise definitions of what constitute bronze, brass and other copper alloys that can't really be mapped onto the copper alloys of the ancient world. That's why archaeologists use the term "copper alloy" these days, means they don't have to be too specific.

There's a very interesting (if you like that sort of thing, which I do) here:-
[url:34qhzybp]http://www.liv.ac.uk/sace/research/publications/Ponting_Archaeometry_MandG.pdf[/url]

Also, it depends on the type of brass or bronze you use for your reproduction. I've seen some items cast from a bronze so red as to be almost copper looking (RQPs bronze is very red) and others that obviously have a higher zinc content and do look like brass but are still classified as bronze according to modern classification.

Location and availability of materials is obviously a factor too. A study of copper alloy artefacts form Northern Britain showed that whilst both types were common, "bronze" items were more common than "brass"; not surprising given that tin was being mined in Britain whereas calamine (zinc ore) would have to have been imported.

[Marcus Mummius]

If you see some roman items with an extraordinary degree of preservation, that even have the original colour, you can see often a yellowish/golden colour. That's closer to our today's brasses than to our today's bronzes, that are more "red" or "copper" coloured.

Roman uses a lot of copper alloys. Sometimes, they have a lot of items for reciclyng, so the final result often was a alloy with a lot of components.

And for some purposes, they add some metals to the alloys. Lead, silver, etc were added to the alloy. That metals were added to change aspects as the viscosity, point of melting, hardness, colour, etc.

The well preserved artefacts that have a golden colour are most likely water and marsh finds. The golden colour cupric alloys get in such a burial context is called a marsh patina. It's an all different story if they are preserved in another context (they won't be golden coloured then).

Like the others said, a lot of recycling was done so a lot of different alloys were used.

The Romans did not make brass but mined an ore called aurichalcum/orichalcum ("golden copper"). In this ore copper alloyed with zinc was present. Adding zinc to copper is a proces that was known probably in Afganistan and perhaps in India, but the Romans most likely did not do this, they just used the natural alloy orichalcum. Brass was often used for military equipment in the Imperial age.

The Romans used alloys with a high copper content and low zinc content to make things like rivets (this alloy is softer and better suited for rivetting than an alloy with a high zinc content). This alloy with a high copper content can be substituted by copper when you make e reconstruction. The appearance is the same.

Most Roman brass also seems to have a lower zinc content than our brass and would have been a bit less yellow than our brass.

I think there is info about this subject in the Lorica Segmentata books by Bishop, you can read the books online here: http://www.armatura.co.uk/

Oh and by the way: in most circumstances archaeological cupric alloys with a high tin content are very well preserved compared to alloys with a lower tin content.

Vale,

[Matthew Amt]

I hadn't heard about orichalcum being naturally occurring! I understood that the Romans made their brass by using zinc oxide and alloying it with copper through cementation (I think)--and no, I don't know how that process is done! If it's natural, shouldn't there still be deposits around today? Could it be that you're thinking of arsenical copper, which was used in the late Stone Age/early Bronze Age? (Though there is debate about whether the ancients actually added arsenic to their copper or not!)

In short, to answer the original question, the Romans used both brass (copper/zinc) and bronze (copper/tin). Their brass tended to have a lower zinc content than modern common yellow brass (70/30), so if you can find "red brass", "low brass", or "commercial bronze" (which is brass, not bronze!), you'll have something closer to the real look. During the Principate, orichalcum was apparently used only for coinage and military gear, while civilian or domestic copper alloy items were bronze. But yes, there was definitely some overlap due to recycling, and any copper alloy items, particularly cast ones, could have varying amounts of lead (as well as other trace elements). Common practice these days is just to call an artifact "copper alloy" unless it has been analyzed to find its actual content.

It is also common just to use modern yellow brass for most Roman copper alloy repros, though many of us use copper rivets (which often were only a few percent zinc). If you can find other alloys, cool, otherwise we don't tend to worry about it much.

Items which are actually supposed to be bronze are more problematic, since most modern "bronze" has little or no tin. The closest you can come in sheet form is phosphor bronze, which has only 5 percent tin. That's fine, but tin content often ran around 10 percent, or as high as 15 or even more for some items. Easy enough to achieve if you are casting your own stuff, but for commercial sheet metal, forget it. Furthermore, phosphor bronze is only made in sheets 12 inches wide! So you can't make a muscled cuirass out of it. Generally folks will substitute silicon bronze or commercial bronze, neither of which actually have tin but they are a redder color than regular brass. It's a compromise.

I wouldn't trust the color of ANY artifact seen in a museum case. There's just no way to tell how it was preserved, conserved, or treated. From what I've seen of how my own brass and bronze items change color just sitting in the air, the only way to tell the item's original color is to clean the surface with abrasives. And that's not usually an option with artifacts! It *is* often possible to see general differences, such as fittings on a helmet being a different color from the rivets that hold them in place. Beyond that, be careful.

Valete,

Matthew

[Marcus Mummius]

Matt, I'll give you an answer on the brass alloys as soon as I have some time.

[PhilusEstilius]

If Roman yellow bronze or brass is anything to go on here are links to a picture of the Trimontium cavary sport helmet. The original and my reproduction which I made in modern 70/30 brass.

http://www.northumberland-computers.com ... oman10.jpg

http://www.northumberland-computers.com ... roman7.jpg

[Doc]

Matt,

I believe you are corret that orichalcum is not naturally occuring. I have personally analyzed roman "bronze" using x-ray fluorescence and the result was NO tin. The alloy had over 20% zinc and the remaining was copper. If there was anything else it was trace.

[Marcus Mummius]

Matt,

I believe you are corret that orichalcum is not naturally occuring. I have personally analyzed roman "bronze" using x-ray fluorescence and the result was NO tin. The alloy had over 20% zinc and the remaining was copper. If there was anything else it was trace.

I've seen and done a lot of XRF analyses of artefacts that did have tin in them. The romans used a wide variety of cupric alloys (Sn, Pb, As, all are occuring components and not just as trace elements).

Also in some burial circumstances the tin can disappear from a cupric alloy by differential corrosion. What kind of XRF did you use? Portable XRF often gives very shady results... The problem with XRF is that there is no good supporting software for the analysis of ancient artefacts. As you probably know (but it might be interesting to people who don't know) the software has pre-programmed standards for modern alloys and it tries to find the modern alloy that corresponds best with the alloy that is analysed. If it can not find a similar alloy in the memory it will resort to giving values in between the measured alloy and the pre-programmed alloy that corresponds best (so this is not the real composition of the alloy you are analysing). You can 'train' the device by doing a lot of measurements and storing all the results but still it's almost impossible to get absolutely correct results.

About the roman brass (Cu and Zn) how do you suggest the romans made this then?

There is a lot of interesting information in Plinius' Naturalis Historiae, the book on non-precious metals.

Vale,

[Doc]

Jeff,

It was not a portable unit. I had found a book in the library where analyses were done of ancient metals including Roman coins and statues. I then selected metals standards based on the metals that were found in that book.

I then scanned the indivdual metals into the computer and set them as standards. I then proceeded to test some of thje Roman brass. I also checked some metals that were pre-programmed into the machine. Either way, there was no tin detected. Only copper and zinc. There were other metals but in trace amounts (less than .5%).

I am an Organic Chemist. I do not deal with metals per se. I did this analysis along with another chemist who specializes in analytical chemistry.

My guess is that their processes were trail and error. As a chemist, I can tell you that trial and error is a big part of discovery even if we are aware of complex chemical theory.

They would mix two metals together and see the result in strength and appearence. We must also consider that for the most part, we may be in the dark with respect to how they did "chemistry". It is probable that different sources contained different quantities of various metals. For example, if I buy chemicals from two different companies, many times the same chemical from one company has a different purity than another company. Since they did not have modern instrumentation to acutally test their samples, they mixed what they thought gave them the product they required. Then depending on the source metal mixtures were obtained.


The fact that many times there are several mixtures of metals does not necessarily indicate that they recyled. This may be one cause, however, in a foundry, if they did not "clean" their apparatus, then the residues left behind get incorporated into the next product.

[Marcus Mummius]

Hi Paolo,

Do you mean that the Romans used cupric alloys that contained no tin, amongst other alloys that contained tin? Of course I fully agree to that.

If you are saying that Roman cupric alloys contained no tin, then you are mistaken, there is a lot of Roman tin bronze known (Cu, Sn and some trace).

Vale,

[PhilusEstilius]

I do have to say Paolo and Jef that you are both talking way above my head on this subject, I do of course respect both of your expertise in what you are both putting forward. What of course interests me about brass or bronze for that matter, is indeed it's malubility for when I have made many things in the past the modern materials I get just don't give me the same results as that achieved by ancient craftsmen. The thing I find today is I cannot get a brass with much lead content hardly even 1.25%, then on the other hand I some times get an old piece of brass from a scrap yard which behaves wonderfully. I have to also say that some material I get gives off a beautifull Green flame when I anneal, and that stuff works well would that green flame be sink I wonder. When one looks at the link I gave to the original Trimontium helmet that I had the pleasure of measureing, the upper third area of that is paper thin, that suggested a very workable brass for the neck guard and peek are around 22 gauge and the top of the bowl is only in the reagion of 5/thou of an inch thick.

[Marcus Mummius]

When one looks at the link I gave to the original Trimontium helmet that I had the pleasure of measureing, the upper third area of that is paper thin, that suggested a very workable brass for the neck guard and peek are around 22 gauge and the top of the bowl is only in the reagion of 5/thou of an inch thick.

Does anyone know the composition of the alloys used for bullet and shell casings? These alloys can be streched a lot without breaking or tearing. It might be that the romans could make comparable alloys.

Vale,

[Apollyon]

Items which are actually supposed to be bronze are more problematic, since most modern "bronze" has little or no tin. The closest you can come in sheet form is phosphor bronze, which has only 5 percent tin.

There are phosphor bronzes with higher tin content; scroll down to "Phosphor Bronzes":

http://www.nbmmetals.com/prod-alloyfamily.html

[Matthew Amt]

There are phosphor bronzes with higher tin content; scroll down to "Phosphor Bronzes":

http://www.nbmmetals.com/prod-alloyfamily.html

Yes, but those don't seem to be available in sheet form. There are certainly uses for bronze rod now and then, but most of us armor junkies are mainly interested in sheet metal!

Hooo-eeee, bronze rod SIX INCHES in diameter!! That'd make a dandy battering ram!

Matthew