Author: Philip Süßer

When the flowers summer rain
are overpowered by sulfur smell
When malachites' green blessing
shines through charcoal dust;
Volunteers great in spirit
rush to help were need is be
Whether bustling, whether tired
lead them on oh Roseman

Today the experiments went into their second round. In order to produce pure copper a second smelting step was needed. In preparation for this step, the bottom of the pit we dug yesterday (let’s call him “Big pit”) was covered with a thick layer of charcoal dust, to prevent that the molten material would react with the clay and be lost in the ground.

While this was done, another pit was used to smelt malachite and reduce it to pure copper. This was done in order to find out whether the right conditions could be met in the pits, and also to experiment with different forms of crucibles. The results varied between “very well” over “molten crucibles” to “crucible too large to properly heat up the inside”.

Last but not least the “Big pit” was fired up. The roasted dungballs were put onto a bed of freshly glowing amber and covered with charcoal. The bellows were worked again in order to reach temperatures around 1400 °C. Unfortunately, this time we weren’t able to achieve sufficient separation between matte and slag to quench the top and take of plates of the iron rich melt. Nevertheless, the experience was valuable. After many hours of bellow working and staring into the flames we only had to clean up and go back to our homes. But for some of us, this was only the beginning…

Author: Philip Süßer

With the slag cake now cool enough, we took it out of the furnace and started documenting its weight and taking samples. Finally, after a quick photoshoot of the cake it was finally time to crush it and prepare it for further steps of the experiment next week.

Since further experiments were planned for tomorrow but also rain was forecasted, we decided to dig another pit beneath a shelter so we wouldn’t be affected by the weather. After lining the freshly dug pit with clay and after 4 days of work finishing the grinding of the matte, we had the opportunity to do what every four-year-old would envy us for. With the freshly ground matte and waterbuffalo manure as fuel we formed small pellets which were roasted overnight to get rid of the remaining sulfur.

Author: Philip Süßer

Since the furnace was still too hot, and the wind too strong for further experiments, we decided to take a fieldtrip to Maria Laach. After a few hours of intensive Cloister-sightseeing and a short Boat trip (during which Thomas showed us that he is not only talented in taking charge of experiments but also of a boat) we finally went back to LEA to continue our work.

With new found energy, and the furnace now cool enough we proceeded documenting the remains and tearing down the front wall to reveal the products inside. Even though the slagcake itself was still too hot to be taken out of the furnace, we were able to clear it from the overlying charcoal leftovers and retrieve some of the loose parts of the slag and the matte.

Author: Philip Süßer

The wheather Gods have been kind to us. Due to the calm wind and generous irrigation of the area surrounding the furnace using the facility-built in rainwater cistern, we were able to proceed firing up the experiment. Before heating up the Mitterberg-inspired furnace everyone got the chance to familiarize themselves with operating the bellows and working in pairs to get a constant air flow into the fire. As soon as the furnace reached a temperature of about 1000 °C practice time was over and the bellows and the newly achieved skills were put into action.

After reaching 1200°C using the bellows, the furnace was filled to the top with firewood and a short while after, the first batch of ore was introduced into the fire and covered again with wood. Subesquently more wood and ore were introduced accompanied by regularly compressing the material already in the furnace. To make sure that the last batch of ore could sufficiently smelt, the bellows were operated for two more hours before finally letting the fire burn down.

In constrast to our previous experiment, we managed to reach temperatures exceeding 1500 °C. Consequently, parts of the inner furnace lining started to melt and caused blockages in the air supply. Keeping the tuyeres free meant extra work for our furnace operator E. Hanning from a relatively early stage of the smelt on.

But not only E. Hanning was running on high temperatures. With a cosy warmth of 40 °C outside, also the bellow operators were getting their share of a good roasting. But plenty to drink and good sunprotection, as well as frequent exchange of the operators were the first priority, the effects of the heat were kept at bay.

To see the fruits of our labor, patience is needed. The furnace is still very hot and will take at least a day to be cooled down enough before it is possible to tear down the front wall and have our freshly produced slag-cake brought to the surface.