Probably a question that gets asked a lot but...
... I'd be very grateful if anyone had any 'dummies tips' for telling the difference between copper fouling, rust and pitting in a barrel.
I'm fairly certain I can identify copper fouling (and I know it's there if wet patches come out blue), but the others I'm not so sure.
I know that in many cases, it actually doesn't make much difference - but it would be nice to know what I'm looking at.