Period: Bronze Age (c. 1700-500 BC), Viking Age (c. 800-1500 AD)
Project title: Bronzestøbning: overfangsstøbning, tabt fedt og tabt bly.
Researchers: The Bronze Casting Group, Prehistoric Archaeology, University of Copenhagen.
E-mail: anettes82(at)hotmail.com
Year: 2007
Abstract:
Even though the constituent components of bronze (copper and tin) do not occur naturally in Southern Scandinavia, an advanced bronze casting technology was developed in the course of prehistory. Unfortunately, there are very few archaeological finds that show how this bronze casting actually took place. The aim of this project is to perform practical experiments with prehistoric bronze casting in order to learn more about this lost art.
In 2007 three main experiments were carried out
Experiment I
A large number of bronze chisels from late Bronze Age have been found. In this experiment copies of the Bronze Ages chisels were constructed and used on different materials such as softwood, hardwood, sandstone and granite in order to compare the wear traces with the wear traces on original findings.
Neither the processing of wood nor stone produced archaeologically found wear traces. However, the chisels were shown to be useful for working with wood, but not for working with stone. Both the granite and the sandstone disfigured the chisels. This indicates that the prehistoric rock engravings were not carved with bronze tools, but are likely to have been carved with harder tools such as stone.
Experiment II
Both Minoan and modern goldsmiths use wax moulds for bronze casting. In this experiment it was to be tested whether other fats than beeswax were usable. Pure tallow proved to be unusable as the material was too soft to keep its shape. Also tallow mixed with wax in proportions 1:1 and tallow mixed with flour proved to soft. A mixture of 1/4 tallow and 3/4 wax, however, showed to be useful, especially for modelling and stamping, but not for carving.
Experiment III
Casting moulds and other casting waste are rarely found in archaeological excavations. The question is whether this is an indication that prehistoric moulds were more perishable than modern moulds. In this experiment moulds were tested that had been fired for a longer or a shorter time as well as a mould that had not been fired at all. All the moulds were exposed to the liquid bronze more than 1100 degrees Celsius in temperature, and the moulds were followingly submerged in water for a year. After one year the moulds were preserved to respectively 100%, 95% and 25% of their original size. The conclusion was that it was indeed possible to cast bronze in unfired moulds, and that these moulds are unlikely to be preserved in the archaeological material.
These experiments form part of an experimental series.
Reference number: HAF 22/07
Project title: Forsøg med bronzealderens støbeteknikker
Researchers: Bronze-casting group, Prehistoric archaeology, Copenhagen University
E-mail: anette82(at)hotmail.com
Year: 2006
Abstract:
Even though none of the components of bronze (copper and tin) can be found naturally in Southern Scandinavia, a very advanced and distinguished technique for casting bronzes was developed in this area during the Bronze Age. Unfortunately, only few archaeological finds tell us how the casting of bronzes actually was conducted 3000 years ago. The aim of the experiments is - through practical experiments - to obtain new knowledge of how the casting was conducted in the Bronze Age. The experiments in 2006 were focused on investigating aspects of the tools used in the casting process – the crucible and the casting moulds.
After several experiments (in 2005 and 2006) testing crucibles with lid, it can be concluded that it is not possible to melt bronze in a crucible with lid or a closed crucible. On the other hand, this type of crucibles can be used for melting of other kinds of metal e.g. tin or lead.
The continued experiments with castings of flat, decorated axes in open clay moulds showed that it is possible, but there are several problems in producing the desired shape and surface. Instead the axes might have been casted in stone moulds and not decorated until after the casting.
The experiments with cire-perdu-moulds (using the lost-wax-method) showed that more work is needed to understand this technique fully. With the lost-wax-method, the artefact is formed in wax, then a clay mould is made around the wax model. Finally, the wax is melted out of the clay mould to make space for the bronze. Possibly, the clay mixture for the mould is not right, and fine-parted organic material (manure) has to be added to the mixture.
Additional experiments with castings in stone moulds with an inset clay core showed some problems with the used techniques, but the experiments had to be stopped before a conclusion had been reached. The experiments will be continued later.
Overall, the group has made valuable experiences that hopefully will make the casting process easier in the future – it seams like the crucibles survives longer when they are not cooled down between each casting, as well as the quality of the casting gets higher when the mould has been warmed up as much as possible before the actual casting with bronze.
Reference number: HAF 11/06
Project title: Bronzestøbning
Researchers: The Bronze-casting Group, Copenhagen, Denmark
E-mail: anettes82(at)hotmail.com
Year: 2005
Abstract:
Despite the fact that neither copper nor tin are found naturally in Southern Scandinavia, and that these wares had to be imported from the south, a very fine and advanced bronze-casting technique was developed in this area in the Bronze Age. Unfortunately there are only few archaeological finds that can tell us how bronze casting was actually carried out at this time. The aim of this group of students from Copenhagen University is to carry out experiments with bronze casting in practice. These will give further knowledge of the subject and also enable refinement of the questions that need to be answered before we can understand how bronze casting was carried out at this time.
Reference number: HAF 11/05