Bronze casting at the Experimental Archaeology Conference

Part of the conference (https://storify.com/artefactual_KW/experimental-archaeology-conference-9) which I attended last week was a couple of hours at the UCD experimental archaeology site, which is a small grassed area beside the campus. Whilst there we watched some bronze casting done using bronze age methods, carried out by Umha Aois: (https://www.facebook.com/umha.aois).

That meant they used bag bellows like this:

And old fashioned crucibles like this, which are handled by means of a wood stick stuck into the handy socket at the back:

which is being used in a furnace in which the air came in from the top through a right angled tuyere.

Sinking the fireplace into the ground has some advantages, such as fairly good insulation and it can be made and prepared quite quickly. On the other hand I do wonder about the limits of the size of melt that can be made, since the crucibles had to be small enough to be easily handled by sticks.

Anyway, here’s the two videos:

It was a nice little axe that they made. The man who broke it out the mould was much more gentle than I would be, I prefer to smash the mould material off it in a couple of goes, rather than gently break it by tapping. Note too that the tongs used don’t quite fit the crucible, which can cause some difficulty in working, but they managed well enough.

Observe too the colours of the charcoal before they remove the crucible from the fire, and the colour of the liquid metal. They had no thermometers, only their eyes and skin, and so experience tells you when the melt is ready.

So, a nice part of an interesting couple of days. I reccomend the conference to anyone, it should be on again next year, although I think the location is still to be decided. Meanwhile I am jealous of UCD for having their own area for experimental archaeology.

Real and possible misperceptions about medieval copper alloy castings

In the rainy season I thought I’d correct a few of the odd ideas that people have about medieval casting, but the annoying thing is I can’t really find many examples of people being wrong. This is in part because the internet is not all powerful and all containing, and searching it isn’t as easy as it used to be. Some of the errors will have been promulgated off internet, in magazines or books that I have never read. Other errors have no exact source, but are what people assume based on partical knowledge.

The most common error is certainly the idea that they used sand casting, especially for cauldrons and smaller items. Apart from the lack of dumps of metal contaminated sand at excavated foundry sites, we’ve got lots of physical evidence of what they did use to cast bells and cauldrons. Yes, clay and organic muck. It survives well in the ground. For instance, at Exeter archaeologists dug up over half a tonne of clay based mould fragments from the manufacture of cauldrons, as can be seen by the shape of the pieces.

Elsewhere in the country many fragments of bell mould have been dug up, whether in London, York or elsewhere. These correlate with areas and times when the documentary evidence shows that there were bell foundries at work, and in the texts they refer to earthen moulds, i.e. not sand, but mixes of clay and other sedimentary materials.

(I just found this report on a Lincolnshire excavation that examined bell casting debris http://services.english-heritage.org.uk/ResearchReportsPdfs/104-2002.pdf)

We also have the remains of a clay based buckle mould found in London, showing that they were using it for small items as well. Since we also have stone moulds which could be used for buckles and the like, the question is, where would sand moulds come into it? Continue reading