What's interesting is that fiat currency has failed for both USA and UK.

Pure silver pound was temporarily suspended, mixing in less precious metals, resulting in failure and inflation. I believe the UK returned to pure silver as a consequence.

I don't know how long the pure silver dollar reigned, after that I guess came a period of gold backing until pure fiat was introduced.

Florines, ducats and gulden became famous and valuable currency for their high gold content, I believe 3,5 grams of pure gold.