‘Darren’ was the process of annealing under extreme heat with a powerful air supply. During the process, a mixture of lead oxide and copper oxide was discharged as slag. This resulted in what were known as ‘Darrlinge’ - parched lumps of copper, largely free of lead, which were covered with ‘Pickschiefer’, a scaly copper oxide. The Darrlinge were quenched in water, and the metal oxides clinging to the surface were chipped off.