01-22-2009, 03:20 PM
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
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
Matthew Amt (Quintus)
Legio XX, USA
<a class="postlink" href="http://www.larp.com/legioxx/">http://www.larp.com/legioxx/
Legio XX, USA
<a class="postlink" href="http://www.larp.com/legioxx/">http://www.larp.com/legioxx/
