These are very preliminary numbers and thoughts.
If you’ve been following along (youtube recorded lecture on earlier research), you’ll notice straight away that this is FAR too little copper based on surface readings of specimens in museum collections, like 15-20% too little copper. I’ve excluded readings with too many light elements (suggesting oxidation and other surface interference) and those with too high of sulfur or other evidence for incrustation. So what’s going on. My preliminary hypothesis is that the conditions of deposit may have been high in sulfur/sulfuric acid resulting in the leeching away of surface copper. The same but also sort of the opposite of surface enrichment (blanching) for silver coins.
My research partner Wayne Powell also reminds me that he would have consider all the Nemi coins to have a patina that will have lowered the copper. I’m curious about the mechanisms for the formation of a patina in such a collection of such archaeological material.
That said the consistence is across issues and internally is is very satisfying. Relative standard deviations are 14 for copper, 25 for lead and 23 for tin. This is far better than for museum collection data where copper was at 21, lead at 38 and tin at 47. The sample set is very internally consistent and that is reassuring.
The next steps are to compare this data to the aes rude and figural votive deposits pXRF readings for the same site. For me this is even more exciting.
The figural votives from the same site have almost the same metallurgical profile as the aes grave:
The relative standard deviation isn’t far off either: 17 copper, 26 lead, 32 tin. Whatever soup was being cooked up to make small cast bronzes be they aes grave or votive figurines it all looks to be much the same.
This is based on 39 readings of 15 figures or figure fragments. Many of the other votive bronzes (nails, tridents, knuckle bone, shell, etc…) seem also to come from the soup but they are more distinctive form and with few similar types to compare. Here is a quick snap shot of everything we tested that wasn’t likely to be monetary object and loosely classified as bronze:
Most could be described as heavily leaded.
The discrepancy between this archaeological data set with readings collected in museums (Rutgers, Princeton, Yale) is interesting and deepens the justification for testing the composition at depth, either by drilling or better through non-invasive exploration. I guess I have some grant writing to do.
Liv Mariah Yarrow 