Image courtesy of Classical Numismatic Group Inc
Peter Northover's analyses of some continental potins (BAR, British, 222, 1992) was useful in that the potins of the Sequani had about the same levels of tin as did the Durotriges "cast bronze". The sequani had the Helvetii as neighbours to the east who also had potin coins but with a higher tin content than the Sequani. This seemed to parallel the Dobunii/ Durotriges relationship with regard to the coin-like tin ingots.
The Zürich type of the Helvetii has tin levels generally higher than the Thurrock potins so if the tin source was also British we might think that the Zürich type would be earlier. In all the analyses, however, whenever we see a trace of cobalt, the traces of nickel are of a higher percentage. Given the date assigned to the Zürich type, if British copper was included in the tin alloy, then we would expect the cobalt/nickel ratios to be reversed.
The most interesting discovery yesterday was this paper by Michael Nick on a very strange hoard of the Zürich type. The hoard is believed to have originally been deposited in the lake because water levels are thought to have been higher when the hoard was deposited than they are now and at its discovery, it was on dry land. What is very strange about it is that the people who deposited those potins attempted to smelt them together in a solid mass by using a hot fire of oak logs. It did not work very well and the effort resulted in a couple of "nuggets", one very large, the other small and some fragments and loose coins. Instead of building another fire to complete the job, they just deposited what they got. It might have seemed too wasteful to attempt it again, or perhaps they thought it just would not work. It certainly seems like they had attempted this task for the first time and had thought it would work much better than it did. The final solution, that it was a religious lake offering, does not ring true to me: in all offerings at "watery places" of which I am aware, this is the only one where they felt the need to melt everything into a single blob. Any sort of "ritual killing" of objects mostly takes the form of breaking or bending. In most watery deposits, however, objects are just cast into the water without being "ritually killed" at all. Presumably, the water "drowns" the object. Although it was recorded that the Celts believed that the soul could be destroyed by fire or by water, this does not fit well with any religious offering and would be more likely to be symbolized in an execution rather than a sacrifice. I mention it only as it does provide a tenuous connection to the find.
I think that the most likely explanation is that we have, again, a time when the price of tin had dropped. We would expect such occurrences in the Iron Age, because the race for tin was all about making bronze for weapons. Phoenician tin traders seem to have been reluctant, at first, to provide Egypt with tin as that would have made Egypt a greater threat, so the Egyptians used copper and flint longer than they might have. There was a great competition for tin in the western Mediterranean, and Massalia had problems obtaining it because of Carthaginian piracy. They imported British tin through an overland route, I think, in the form of Thurrock potins which bore the same images as the Massalian bronze coinage of the time. Massalian bronze coins had the lowest percentage of tin (about 2%) of all of the Greek issues and has tested positive for the British high cobalt to low nickel "signature". The only other continental example being a cauldron with some sort of British association that was, interestingly, found in Switzerland. Iron weaponry was now preferred, and there was no shortage of old bronze weapons that could be recycled to meet the need for that metal. I think it is possible that the people wanted to hoard the potins for their metal value, hoping that the price of tin would recover later. Instead of burying them, they might have decided that the lake would make a good hiding spot, and that by melting them together it would make their recovery easier through a joint effort, but less likely to be raided by individuals who might dive for the potins. I cannot see any indication that this action was a local religious custom: it was a flubbed attempt that was not even corrected. One of those things that seemed like a good idea at the time.
I plan to wrap up the series on Monday, but we will see... . Have a great weekend.