red brass

[Marcus Mummius]

Salvete,

Has anyone worked with 'red brass'? This is brass with more copper and less zinc in it than yellow hobby brass. Roman brass was more like red brass than like yellow brass isn't it?

Is red brass stronger or weaker than yellow brass?

Valete,

[Marcus Mummius]

And another question:
Matt Amt says on his site that things like helmets and lorica fittings were mostly made out of orichalcum with a zinc content of 15-20%.
Is this indeed the case for most lorica fittings? Are they of a more reddish colour than modern yellow hobby brass? I've seen a few original hinges but most were very yellow...

Can someone help me with this?

Thanks in advance,
Kind regards,

[mcbishop]

First, take a look at (and bookmark) http://www.anchorbronze.com .

This is from my Lorica Segmentata vol. 1 (page 77):

The copper alloy used for most of the fittings (hinged fittings, lobate hinges, tie loops etc) was a type of brass known as orichalcum, the same metal used in brass coinage from the time of Augustus onwards.6 Orichalcum, which is almost golden in appearance (Plates 1 & 4), was a binary alloy of copper (80–85%) and zinc (20–15%) and was quite widely used in military equipment from the 1st to the 3rd centuries AD. As such it closely resembles the modern alloys of ‘low brass’ (CA240) to ‘red brass’ (CA230) (with a Rockwell hardness of between 70 and 65). Since orichalcum was also used in currency, the components of lorica segmentata made from it were, effectively, constructed from bullion. The rivets used to secure the fittings to the iron plates might be of the same composition, but a softer metal was often used, with between 90/10 composition (‘commercial bronze’ (CA220), with Rockwell hardness of 58) and 95/5 (‘gilding metal’, CA210, with a Rockwell hardness of 52),7 which made it easier to secure (peen) the rivets in place. The higher copper content of the rivets also gave them a more coppery colour. No examples of bronze fittings (i.e. a copper/tin alloy) have so far been identified on Corbridge-type cuirasses.8 The different colour characteristics of the various metals means it is often possible to identify uncorroded metals tentatively without the aid of any scientific analysis (the Newstead fittings, for instance, are brass-coloured, although they have never been tested), but such analyses are obviously desirable in the long term.

Does that help?

Mike Bishop

[Matt Lukes]

Hi Jef,

I've never worked with red brass so can't really answer your first questions directly, however the data I've found gives tensile strengths of red brass (UNS C34000, 85:15 Cu:Zn) vs. half-hard yellow brass (UNS C26000 70:30 Cu:Zn) as 40000psi and 62000psi, respectively. So it would seem that red brass is rather softer than yellow brass.

As for your second question, it has been my impression that original military objects such as balteus plates, buckles, pendants and segmentata hinges do indeed seem to be made of orichalcum that isn't significantly different in appearance from modern yellow brass. I have removed at least a tiny spot of the patina in an inconspicuous area on all my artifacts now to reveal the actual metal, and it all looks just like the yellow brass I use for my replicas to me.

Red brass seems to be used mostly for plumbing pipe- one of the largest manufacturers of copper and brass in North America only offers red brass as pipe- and from what I recall when I've seen it in the past is that it is more of a gold color- clearly different than yellow brass. So, my thinking is that modern yellow brass is indeed the best material to use.

Matt

[Marcus Mummius]

Thank you very much to you both! Very helpful. I noticed that brass sheet with a brass content of a bit above 80% was offered by a german store:

http://www.reenactors.de/shop.html

First click 'Warenangebot' on the left, then click 'Ausrüstung und Zubehör' just under 'Neu bei Reenactors'. The 'red brass'(it isn't that red mind you, more dark golden) is just below the fire arrow, it goes by the name of 'Tombakblech'.

Here's a link to just the picture of the sheet brass: http://i6.photobucket.com/albums/y233/M ... tbrass.jpg

Do you guys think this material would be more authentic for things like seg fittings and buckles than yellow hobby brass? I think I read somewhere that florets were made from brass with more zinc (more or less the same amount as yellow hobby brass).

Should one bother to use this material for some items and yellow brass for others or isn't it worthwhile?


Kind regards,

[Matt Lukes]

Should one bother to use this material for some items and yellow brass for others or isn't it worthwhile?

Well like I said, all the original pieces I have in my collection don't look significantly different from regular 70:30 yellow brass, so I don't see any reason to go to the trouble and expense to get brass that has a slightly lower zinc content unless your intent is to go for metalurgical accuracy over all else.

It seems to me that a variance of 5% among the sample of metal tested isn't exactly small, so makes me wonder just how strict the 'recipe' for making brass really was anyway. It must also be borne in mind that if the sample population that resulted in the 15-20% zinc-content data was small, it may not be reasonable to take it as anything other than a very general idea of the composition of orichalcum.

I have a couple of orichalcum coins (a Dupondius and a Sestertius) that, judging by their colors, appear to have quite different zinc contents; one is quite yellow- moreso than modern yellow brass- and one that is rather red-gold, so I'd bet their zinc contents are outside the 15-20% range.

Mike- do you know how many pieces were tested to yield the 15-20% zinc range you mention?