There were three types of currency in the Great Han Empire: gold, silver, and copper coins. Copper coins were an alloy of copper, aluminium, lead, and nickel. The production of copper coins were completely managed by the imperial court. The local authorities and the wealthy did not have the right to manufacture copper coins. That would be a heavy crime, and it was rare for anyone to want to take such risks.
But gold and silver coins were different. These two were precious metals. If the local governments and wealthy people had enough gold and silver, they could melt and create their nuggets. This would create a lot of chaos. Quite a few greedy people mixed metals that easily mixed with silver such as lead and aluminum into the nuggets.
