I have been volunteering at the Portable Antiquities Scheme since the 3rd March, identifying and recording archaeological finds. My work for the PAS has brought me up ‘close and personal’ to bronze and other metal objects, but despite this, I really didn’t know anything about how they were made. It was then decided that there was no better way to learn about bronze smelting than on a warm May day. This training day was run by Mark Vyvyan-Penny and Bill Crumbleholme, two seasoned craftsmen out of Weymouth. They were to guide us through two methods of smelting.
The first smelting process we did was involved casting tin in a plaster board mould. We were given two squares of plaster board, of which one would be our canvas. Using cocktail sticks and small dental instruments, we carved whatever shape we desired into the plasterboard. I chose a six pointed star, but others around me chose flowers or a variety of animals. Each shape had to be carved into the plasterboard, approximately two millimetres deep. In my eagerness to carve channels for the tin to flow through to all the compartments of the six pointed star, I carved through the plaster board. This was easily fixed by placing the previously discarded paper onto the back of the mould and fixing with glue. Once the shape was finished, a sprue (a triangular incision) was carved, connecting the edge of the plaster board with the mould. This would ensure that the melted tin would flow freely into the desired shape, provided the channels had been adequately dug.
In order to heat up the furnace, each volunteer took part in pumping the bellows. Mark made it look so effortless with one hand, but most of us had to contend with using two. The influx of hot air was vital to the furnace achieving and retaining the temperature needed to melt tin. As it melted, we all watched anxiously as Mark poured molten tin into the moulds, and almost all were rewarded with the tin fruits of our labour.
The second smelting process was a lost wax method, unsurprisingly named for the wax mould melting away to create a vacuum for the molten bronze. I made a ring, a simple shape which when covered in the earthen clay would allow the bronze to flow freely within the vacuum that the wax created. A lot of clay was needed to cocoon the mould sufficiently, resulting in the dirtiest hands and a collection of what resembled hand grenades waiting to be fired.
To make bronze, we added rock-crushed malachite (copper carbonate) from Morocco to tin. This was then added to the crucible (ceramic container) within the furnace, which then formed bronze. What was meant to happen was that all the lost wax mouldings would be cast in bronze, but the untimely demise of the crucible necessitated the reheating of the tin furnace. I felt this was the most important aspect of the training session, as it reminded everyone there that despite technical skill and expertise, something could still go wrong. A collapsed crucible really loans perspective to every bronze artefact that was successfully made.
Whilst we waited for the bellows to reheat the tin furnace, a few of the group helped Bill with filing rings school children had made earlier. Others drank tea, and warmed themselves in the heat of the sun and by the furnaces. I thoroughly enjoyed this training session, and now hold a keener appreciation for the craftsmen of the artefacts I now handle.