How was the exchange rate determined between different commodity currencies?
E.g., country X mints gold Zorkmids, each weighing 5g, and country Y mints gold Zennys, each weighting 8 grams. When Ms.XX travels from X to Y, she exchanges her Zorkmids for Zennys, and when Mr.YY travels from Y to X, he exchanges his Zennys for Zorkmids.
My question is: how was the aforementioned exchange rate (8:5) affected by the non-physical circumstances I neglected?
E.g., relationships between X & Y - war vs. peace, amount of trade/travel between them.
What if the king of X imposes a ban on exporting gold coins?
How would that affect the exchange rate? What could the fluctuation be? E.g., can one lose 20% of value because of the exchange rate?
What if the king of Y declares the existing 8g Zennys "invalid" and issues "new Zennys" of 6g - have something like that ever happen? (this is not debasement, the new coins have a new name, new stamp &c). How would that affect the exchange rate of the "old Zennys"?
Obviously, melting one type of coins and minting the new one (don't you need the kings permission to do that?) is an arbitrage opportunity which would limit the fluctuations of the exchange rate. How much?
If it matters, I am interested in, e.g., these times and places:
- "3 musketeers" - 17th century Western Europe
- 2nd-5th centuries common era Middle East (Judea & Babylonia)