Huh. Does that mean they can instinctively fill them? I thought that was one of the distinctions between allomancy and feruchemy, that allomancy is kind of instinctive? Does that mean that Vin didn't have to try all the different alloys to find duralumin, she could have just had Sazed touch them and see if he could fill them?
Yet more evidence that Vin didn't think of everything.
She also didn't understand feruchemy very well.
Actually, I doubt Sazed did either. Feruchemical knowledge was very uncommon, and I doubt they thought any more about possibilities of new metals than allomancers.
Ironically enough, the seat of all Feruchemical knowledge may just have been the Steel Ministry.