In this case coinage is free but not gratuitous.

In this case no bullion is brought to the mint unless the coined pieces the owners receive have a value equal to the bullion value plus the seigniorage charge.

The power to impose a seigniorage charge is a monopoly power.

Artificial limitation is present.
Evidently, the number of coins that can be issued without depreciation is limited to that number which would circulate if they were made full weight without a seigniorage charge.[7] This number of pieces of full-weight metal is the saturation point of the money demand of the country.

If more than that could in any way be put into circulation it would become worth less as money than as bullion, and would be melted or exported.
Assume that this full supply of money at a given moment is 100,000 pieces or dollars; then consider the effect of imposing a seigniorage charge of ten per cent on further coinage.