In the last week of June, the great moment had finally come: One of the furnaces was operated for the first time! A batch of roasted ore was little by little placed in the preheated furnace, alternated with layers of wood. We operated the bellows about 3.5 hours and reached more than 1400 °C in front of the tuyeres. During this furnace campaign, nearly 240 kg of wood were consumed. After the bellows stopped, it took one day until the remaining charcoal had cooled down enough to remove it. The slag cake took another day to cool down. And even then the furnace walls had the cozy temperature for an oven in cool winter nights. We crushed the slag cake and separated the matte from the slag. Although the temperature distribution within the furnace was less than ideal, separating the matte from the slag was easier than expected.
During cooling of the furnace we took two hours to dig a fire pit and lined it with clay to use for the experiments with malachite ore. We heated the pit slowly to dry the clay. During this time we prepared crucibles of different shape and placed them on the margin of the fire pit to dry. After one or two hours we established a bed of charcoal in the pit and filled the crucibles with ore and charcoal. The crucibles were placed in the center of the fire pit and special care was taken that they were permanently surrounded by glowing charcoal. This was important because otherwise the oxygen from the air will oxidize the melted ore immediately and we won’t be able to produce copper. After about 20 min the ore in the crucible was molten. We quenched the crucibles in a pot of water revealing the shiny red of the copper in some of them, indicating our successful conversion of the malachite.
