Originally posted by The Phoenix:

Something I dont understand.
So you get say Copper Ore. Copper Ore Weighs 10 pounds
You put it into the thing to melt it down and remove the Impure parts
of the Ore. SO your taking away some Weigh of the Ore.
BUT As soon as it becomes a Bar. It Gains 2 pound making it 12 pounds
Where the 2 extra pounds come from?
it should not be heavier. It should be Lighter if not , then the same weight.

Having a course of Metallurgy in my Bachelor studies, things like heating time and speed, highest temperature and time it remains there, cooling time and speed, the material that is used to heat and melt the metal, the chamber where it all happens, can change the properties of the produced steel, so I can only assume (without having studied/researched further) as I remember that some C (carbon) is mixed in with the Fe (iron), it could result in a weight increase and coal is about 50% Carbon.