I purchased a sestertius this evening... the description refers to it as a "orichalcum sestertius" ... (I won't show the coin until I receive it). Wikipedia has the following line: In numismatics, orichalcum is the golden-colored bronze alloy used by the Roman Empire for their sestertius and dupondius coins. The other sestertius coins I have purchased have referred to them as brass.. Just curious as to what this term really means...
Generally, the term is used to designate a copper alloy containing zinc, which in other contexts would be refered to as "brass." If you want to know more, this publication might be interesting: E. R. Caley, Orichalcum and Related Ancient Alloys: Origin, Composition, and Manufacture. New York 1964, online here.
Clavdivs, Orielensis is right on. In short, if copper is alloyed with zinc you get brass (orichalcum) & if the copper is alloyed with tin you get bronze. Both metals usually have a small percentage of lead also.
The alloy that Sestertii were made of changed during the first two centuries (there was less tin used during the late 2nd century) and Sestertii were made from bronze after the early 3rd century. This is what pure Orichalcum looks like:
A while back I got a harshly cleaned sestertius of Antoninus Pius and a harshly cleaned as of Faustina I - my photos are over-exposed, but you might get some idea of the difference between the brass (orichalcum) and the copper: The problem with most of these is that the patina obscures the original color.
M.Mike is right. Unfortunately as time passed the difference between red copper and yellow brass became less obvious so our catalogs often list coins as 'dupondius or as' especially when the ruler is a Caesar or Augusta who did not wear a radiate crown under any circumstances. For example, is this Commodus as Caesar an as or a dupondius? I will not be removing the patina to be sure. Some sestertii (by size and weight) have toned brown with a hint of red. We do the best we can to keep things straight. ...but it is easier when they stay yellowish. Both were the same color back when they were made.
i figure if the coins color(under patina) is just so dang purdy ya can't stand it, it's orichalcum Faustina l Dupondius/As..
A key point being lost here is that orichalcum was a naturally occurring alloy. It was mined as is, but was not understood to be brass in the modern sense, at the time.
Curious about that. I understand Electrum is/was a naturally occuring gold/silver ore. However, I understood Orichalcum was brass made by the Romans to give a gold luster to the coin, and increase its perceived value due to its color.
Original sources of orichalcum were found as a naturally-occurring alloy, just like with electrum. For both alloys, it was later discovered how to produce them industrially.
Are you sure that orichalcum occurs naturally? Wouldn't the Greeks have used it to make coins if it did?
I can't find any place where orichalcum (brass) occurs naturally. It is actually harder to produce than bronze, and it was first made in India. The melting point of zinc is much higher than tin, so the alloying process requires a special type furnace.
It shouldn't take a special type of furnace. Zinc melts at 787 degrees. A charcoal fire would do that.
