Salem

What happens if I mix copper ore with iron ore?

What if a smelter has like 99% iron bar left in it from previous smelt of pure iron, and then i suddenly switch to copper ore- does that 99% iron remainder transfer to my copper smelt?

Yes, when it's time for a bar to be made, the smelter looks at what ore is in the spot the bar will go and makes that type of bar. So, if you have smelting progress from iron ore and load up with copper, you'll get copper bars.