The coolest solution I heard was to look at a well defined spot of the gold bar and register the impurities/bubbles/structure that naturally happen while castin

The coolest solution I heard was to look at a well defined spot of the gold bar and register the impurities/bubbles/structure that naturally happen while casting. This is very difficult to reproduce (because there is no legitimate need to do so) and is already present. Edit: And of course put the info on block chain.