When the Bronze is Like a Mirror

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Categories: Ancient, Not an expert

In April I participated in a prehistoric bronze-casting workshop with Dr. Bastian Asmus at the open air museum at Heuneburg (near Herbertingen, Baden-Wurtemburg, Germany). I believe that it is helpful for historians to understand the world of things and skills in which their subjects lived. Like any other art, imitating historical bronze-casting requires a range of skills and is best learned by practice.

Das Donautor

One can make a good case that Heuneburg was the first city in northern Europe. There was an acropolis overlooking the Danube about three hectares in area with large houses and workshops, a middle city, and a lower city of about 100 hectares where most of the population lived. In the sixth century BCE the acropolis had a mud-brick wall on a stone base (Gr. sokle) while the rest of the city was defended with embankments and earth and stone piled inside wooden frames according to northern custom. The leaders of Heuneburg must have been proud of themselves, as they ruled the biggest settlement they had ever seen. Massilia or Veii, let alone Carthage or Athens, were far away. Like the fathers of many early cities, their dream ended suddenly in fire and was followed by a long period in which a much smaller population dwelled at the site.

SAM_2750 Heubeburg from Modern Ground Level
I think that the reconstructed wall and workshops are placed at roughly the level of the ground in the sixth century. Perhaps coincidentally, this makes the wall wheelchair accessible.

I did not take any photos of making the wax models. Bracelets are easy to make by rolling a lathed dowel along a strip of wax to create slopes and lines. A few minutes with a pointed tool adding cross-hatching and dots gives a good imitation of many early pieces. Rings and pins can be made by rolling strips of wax and fusing their ends together in the warmth of the sun. Anything with a socket is tricky, and only one person tried to make a socketed axe.

We kneaded powdered clay, ground pottery, water, and chopped wool to make the moulds. Some people prefer to use horsedung as an organic component.

SAM_2764 Moving Moulds
The moulds need to be fired to harden them. When it is time to remove them from the fire, two sticks work as well as a pair of tongs.

SAM_2767 Moulds in Kiln
A kiln with a slow fire helps to gently dry the mounds overnight. As it happened, the fire went out early.

SAM_2771 Casting Area
The hearth is not just good for warming moulds.

SAM_2797 Self at Bellows
Bringing the crucible up to heat requires many minutes at the bellows and lots of large lumps of charcoal.

SAM_2783 Purple Flames
A charcoal fire fanned with bellows is a colourful sight. When the bronze is ready to pour, it has a smooth, dark orange surface like a fiery mirror. A few pokes with a stick help to determine if the contents of the crucible are liquid without disturbing the coals on top, and help clear cinders out of the crucible when it is ready.

SAM_2786 Raking Out Cinders
An iron hook helps to remove the last few cinders from the crucible, and iron tongs to manipulate it. Before iron became common, smiths probably handled their crucibles by gripping them between branches.

Casting bronze by hand is not certain: the mould can break, it can partially fail and produce a lumpy bronze, it can fail to reproduce the details on the wax model, and the bronze can cool before it fills the mould. Three of our eight castings had significant problems.

SAM_2791 Breaking the Mould
The moment of truth. This year’s broken mounds and crucibles give material for making the next batch!

SAM_2798 Sandstone Mould
Stone moulds can be reused, and work well for large, flat objects. Casting a slender sickle blade is risky.

SAM_2801 Sandstone Mould Open
Air channels reduce the risk of air pockets preventing the metal from filling the mould.

SAM_2803 Things Cast
Two knives, two arm rings, a finger ring, a sickle blade, and a socketed axehead. Another axe-head without a socket is not shown. Now the casting funnels must be cut off, and the bronze needs to be polished and fitted with any non-metallic components such as handles or stones.

Further Reading: Jeroen Zuiderwijk, “1501 BC: Bronze Casting” (Link), Bastian Asmus, Archaeometallurgie (Link), and the Freilichtmuseum Heuneburg (Link).

4 thoughts on “When the Bronze is Like a Mirror

  1. Bastian says:

    Sean,
    I like the post. Thanks for the effort. I hope we mmet again..

    Bastian

  2. Pen Name says:

    In this case they were obviously trying to recreate the entire scenario with historical accuracy. Even with double Acting European Style Leaf bellows you see the fire panting as the flow of air gets interrupted, compared to the Oriental double acting piston in a box equivalent. Modern blacksmiths tend to use hand operated rotary turbines to keep a constant high flame when heating metal.

    https://www.youtube.com/watch?v=X_Jdf5Ab6PM

    1. Sean Manning says:

      Someone I know gave up on bronze casting with historical equipment because it was just too much of a time commitment to keep good enough to continue to be successful. And there are other trades where the historical solution requires 3 or 4 assistants which is just not practical today.

  3. Insights from Experience, Excavation, and Reconstruction | Book and Sword says:

    […] Heuneburg in Germany, a high-status grave of the sixth century BCE has been found near where another high-status grave […]

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