This is a proposal for a new building, called Mint. It transforms part of the shield production into gold.
Currently there is Coinage for that. But it converts all production into gold, and you can change production at any time.
Researching Economics (or Currency, or some other tech to be defined) would enable Mint and OBSOLETE Coinage.
A Mint would transform a certain amount N of Production (it could be hardcoded or ruleset defined) into Gold. For example, let's say N=10.
In a city with +8 Production, a Mint would yield +8 Gold. The remaining Production would be 0.
In a city with +12 Production, a Mint would yield +10 Gold. The remaining Production would be +2.
Several Mints can be built in a city (the building is not unique). That way, you can build 3 Mints in the same city, for example.
In a city with +8 Production, 3 Mints would yield +8 Gold. The remaining Production would be 0.
In a city with +42 Production, 3 Mints would yield +30 Gold. The remaining Production would be +12.
A Mint would have, for example, Cost=30 and Upkeep=0.
Mints can be sold at any moment for the money they cost to produce.
alain_bkr 
This is a proposal for a new building, called Mint. It transforms part of the shield production into gold.
Currently there is Coinage for that. But it converts all production into gold, and you can change production at any time.
Researching Economics (or Currency, or some other tech to be defined) would enable Mint and OBSOLETE Coinage.
A Mint would transform a certain amount N of Production (it could be hardcoded or ruleset defined) into Gold. For example, let's say N=10. In a city with +8 Production, a Mint would yield +8 Gold. The remaining Production would be 0. In a city with +12 Production, a Mint would yield +10 Gold. The remaining Production would be +2.
Several Mints can be built in a city (the building is not unique). That way, you can build 3 Mints in the same city, for example. In a city with +8 Production, 3 Mints would yield +8 Gold. The remaining Production would be 0. In a city with +42 Production, 3 Mints would yield +30 Gold. The remaining Production would be +12.
A Mint would have, for example, Cost=30 and Upkeep=0.
Mints can be sold at any moment for the money they cost to produce.