Diocletian ordered that manuscripts and texts that dealt with the "art of making gold and silver" should be destroyed. Is this what you're referring to?

If so, it's my understanding that this was done as a preventative measure to suppress the growing wealth of some who were able to passably show off imitations of gold and silver as genuine to buyers. Thus protecting Roman power and influence in the region.

This happened in a period of time that I am unable to pin down any more closely than between 290 and 296 AD.