Good morning and (may it be a) happy New Year (for us all). I’m not on holiday as I had expected and am trying to ease myself into work and remember what I love about it. When I need to do that I often look at pictures to see what I see. I decided to look at aes grave in recent trade and this specimen caught my eye.
What specifically caught my eye was the apparent indentations surrounding the lower (in this image) part of of the fulmen (thunderbolt). It’s a curious hollow such as I don’t seem to remember seeing. It seems it must be a feature of the casting process, but how? its sits directly above where we commonly find the spue on this type.
As I’ve said elsewhere (here? certainly in my forthcoming metrology chapter…), cast coins have innies and outies just like bellybuttons. This is how the bronze flowed through the mould via these channels. When the coin is taken out of the mould in most cases either a little of the coin is removed (innie) or a little of the spue remains (outie). Among other things this means that the spues tell us very clearly the alignment of the two halves of the mould were aligned. Given this it seems really silly that we almost always photograph the fulmen in a vertical rather than horizontal position. The creators of these coins meant the fulmen to be on the same axis as the dolphin. Interestingly, when museums record the so-called die access for these specimens in their databases, the belief that the fulmen should be either horizontal or vertical effects how the axis is recorded. Some call it 12, some three, but in all cases the same alignment is being described. (I downloaded the CRRO data and when viewed as a spreadsheet this leaps right off the screen. More on this data set below.)
This spue pattern is so consistent on this type that when it is absent or significantly misplaced, I start to get suspicious. See the below specimen. Notice that the break (innie) is on the top and that there is no exit channel opposite. Notice also have the specimen has a strong join rim all the way around which is highly unusual for specimen of this type. The fulmen is also rendered in a radically different style (the center of the five spikes on each end is distinctively thinner and ends in an arrow in most cases). The fashion for imitations in the 19th century was very strong indeed and their manufacture is a personal point of interest. I have a hunch or inkling (not yet a theory or hypothesis) that engraved illustrations from early numismatic literature often influenced how imitators carved their molds.
My interest in spues isn’t really about authentication of specimens though. Authentication comes through well documented archaeological provenance (but we can talk about that at length). It started because the significant size of the spue, be it positive or negative, can significantly skew the weight of the individual specimen, especially in the very small denominations (unciae, semunciae). The Roman seem to have been remarkably tolerant of weight variations for coins from these earliest series right through to their batch control of the denarius in the late republic (cf. Stannard on gouging). This tolerance is at variance with an understanding of the face value reflecting an intrinsic value of the coin. And I find this apparent double think with Roman’s relationship to money absolutely fascinating. They seem to care about the purity of silver and the heft of a piece of bronze, but only up to a point. Specimens of different weights clearly circulated together. We don’t have evidence of clipping or shaving. Face value seems for all practical purposes far more significant than fabric.
The other thing I really like about spues is that they are a very obvious artifact of manufacture and thus offer us some clues about the creation process and I think they hint at aspects of the likely metallurgical composition of the bronze.
One fact that I can’t get out of my brain is the high lead content (~20-30%) of the Roman currency bars tested by the BM in the 1980s (see Burnett, Craddock, and Meeks). I am on record as being intrigued by the possible parallel metallurgical ratios seen in the Egadi rams (from only preliminary testing). I’m also on record as suggesting that those five pound bars are best associated with the 1st Punic War: This makes them later than RRC 14, 18, and 19. Lead makes the bronze more brittle once cool, but more viscous in the casting process. Specimens invariably show both an entrance and exit channel for the molten bronze (the spues). The Roman valued the ability of the bronze to flow both in and out of the moulds filling the whole cavity. They tolerated the brittleness that left the innies and outies on each specimen as they broke the coins free of the moulds. Heck, maybe the brittleness was even a feature rather than a flaw for this particular operation. Of course, I’m just speculating RRC 14, etc… have a lead content similar to the currency bars. I’ve not YET been able to test any specimens, but that is high up on my wish list.
In private conversation with someone who has spent many many more years than I looking at cast coinage, I’ve heard it speculated that the moulds might have been single use and clay because of how one does not find mould links like one finds die links for struck coinage. The question of materials used for the mould is fascinating. I don’t even know if it is possible to cast this type of bronze in clay. I also wonder if they were made out of clay why we couldn’t find stamp links. This is the age of petite estampilles on fine blackware, so the advantage of a reusable stamp would have been obvious those creating clay moulds. Tufa would be too soft, surely (?!). Travertine? But so often that has a texture of its own. I have questions. FAR too many questions.
Where does that leave me with this first specimen and the funny cavity… Worried. There is no exit spue opposite the cavity, only a smooth edge with a distinctive join. Also that’s a heck of a lot of negative space between the edge of the mold and the central arrow of the fulmen. Definitely funny. Could it be the last specimen in a line of specimens being cast in sequence? I guess. Maybe… But would that work if you were pouring molten bronze into the top channel how would you be confident that the bottom mould filled properly? wouldn’t you need an air hole at least? I’ve got stuff to learn.
What to make of this?
At this point I decided to get a little more serious about these questions so I reviewed all the RRC 14/3 specimens in CRRO and took notes on the spues visible in the available photographs and also any unusual features.
When I’m confident in what I’m seeing on the specimen only 16% have one spue, rather than two, or to be more literal, I found four specimens out of 25 where I am am certain the specimen only has one spue.
The last causes even more concern as the alignment of the spues is atypical. On the dolphin side instead of aligning with tail or head, the spue is at about four o’clock.
The other fun point of note is the Badian collection specimen (Rutgers) has the dots above the dolphin rather than below and seems likely to be an imitation.
Unfortunately most imitations are not this easy to spot. (And, of course it is even just possible this is an engraving error at the mint).
Ideally the analysis would be restricted to specimens from well documented hoards and excavations, and yet that reduces the pool to an unmeaningful sample size.
I will keep thinking….