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Bronze casting


photo by Hans Splinter

 
The people in the bronze age didn't have modern furnaces, thermometers etc. The only things the bronze caster had to work with were the materials he could take from nature, such as wood, leather, clay, sand and stone. Yet with these simple materials, the bronze caster could make amazingly advanced metalwork. In order to be able to do this, the bronze caster had a vast amount of knowledge and experience. To start, the bronze caster needed a fire much hotter then any ordinary wood fire. Then the metal has to be heated and taken out of the fire, and cast in the desired form, with a high quality finish and no defects.

I started casting bronze late 2003 and have been casting frequently since. On this site I'll describe some of the knowledge I've build up. Below is a description of the casting process. For those interested in starting casting themselves, please read the safety tips here first.


The equipment


photo by Hans Splinter

The photo above shows the equipment used in casting. It's partially based on finds and pictures. But as no complete sets have been found, the gaps had to be filled in. For those interested, a detailed description of the equipment can be found in the link below.

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Smelting


photo by Hans Splinter

In order to be able to cast the bronze into a mould, it first has to become fully liquid. Pure copper melts at 1083°C, and mixed with 10% tin at around 1000°C. The bronze has to get well above its melting point to be liquid enough to fill the mould. So the fire has to be at least that hot. This means that the fire above the crucible has to have an average temperature of 1100-1200°C continuously during the melt. This is achieved with charcoal and bellowing air into the fire. As the crucible is buried in the charcoal, the bronze can't be seen. So to check whether the brons is liquid, a thin stick is used to feel inside the crucible. Depening on the amount of bronze, it takes about 15-30 minutes to melt the bronze.

Casting
 

Casting a bronze sword
Cooling the mould
Inspecting the cast

When the bronze is fully liquid, the crucible is lifted from the furnace and the bronze cast into the mould. This has to be done very quickly, as there's only seconds time before the bronze solidifies again. To gain some time, the moulds can be preheated. This is especially important for long, thin casts such as swords, where it takes more time to fill the entire mould. After the bronze has been cast into the mould, the bronze first has to cool down until it no longer glows, as when it's redhot the bronze is very fragile. Then the mould can be opened. If all the steps in the process are performed well enough, and the bronze gods are in a good mood, the caster will find a new bronze casting in the mould.
 

 Finishing

After the casting, the long and hard work of finishing the casting starts. The feeding channels, flash etc. have to be ground away, and then starts the grinding, polishing, sharpening, hardening of the bronze and the making of the non metal parts such as hilts, all of which can take days or even weeks. Eventually after long hard work the a shiny new bronze product is ready. The results of my efforts can be found in "BRONZE REPRODUCTIONS" in the top menu.