He describes his process here. I particularly liked this bit (translated from German):
Fiat in the fireA central element of my work is the melting of old euro coins. In a cleaning process, they are converted into something new by fire – a kind of catharsis. Fiat money, the symbol of trust in centralization and control, is transformed into a new form – detached from its original value, as a reminder of what we leave behind. The processed pieces clearly bear the traces of this metamorphosis – deformation, heat, change. They represent the transition from the old monetary system to Bitcoin.