When the Bronze is Like a Mirror

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.

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.

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.

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.

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

The hearth is not just good for warming moulds.

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

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.

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.

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

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

Air channels reduce the risk of air pockets preventing the metal from filling the mould.

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).