6) With the onset of the Great Depression, FDR was elected for change. One of his first acts (by presidential order) was to change the way the dollar functioned. Silver Certificates were no longer honored. (I am not sure if there were ever gold certificates.)
There were gold certificates and they were called in at this time. Silver certificates were honored (redeemable as actual silver coin or bullion) until 1968 when they effectively were converted into Federal Reserve Notes (common paper money with no silver backing.)