To address the first question: blacksmithing varied by time based on the available skill, resources, and technology. The kind of blacksmithing that took place in Greece 2,500 years ago, for instance, is a far cry from the kind of blacksmithing that took place in Milan a mere 500 years ago.

So, first off, the most important: available resources. It doesn't matter how talented your blacksmiths are: if you don't have access to iron, you can't make iron or steel goods. The Japanese encountered this problem. While they didn't lack iron entirely, the relative impurity in Japanese iron (and the relative scarcity of it) meant that the Japanese used iron and steel much more sparingly than their European counterparts. And the fact that their iron ore was so impure meant that, in order to get a proper steel weapon, they had to fold the iron approximately three bajillion times in the forging process. Hence the seemingly endless folding that takes place in the traditional construction of a Japanese katana.

Other cultures simply didn't have the technology necessary. The native peoples of North America, for instance, appear to have lacked the understanding to smelt any alloys at all -- which means that bronze (copper + tin) and steel (iron + carbon) weren't made. With the exception of iron that quite literally fell out of the sky, these people had no meaningful access to bronze, iron, or steel. And since the United States produces a fair amount of iron ore, we know this is a technological limitation rather than a resource limitation.

Finally, there's the matter of skill. Different metals were produced in different ways at different points in time. Take copper and bronze, for instance. When iron was finally "domesticated," this allowed permanent casts to be made out of iron and used for the casting of copper and bronze. This made the process of turning copper and bronze into something usable much less labor-intensive, which meant you could produce more things in a shorter period of time. Casting definitely took place prior to the use of iron for permanent casts, but this casting would've used sand molds and the like -- molds that were rendered unusable after a single use. To put the comparison into modern terms, it's kind of like only having access to paper plates (made by you or your neighbors) and then suddenly being able to buy washable and reusable ceramic plates.

This is really just touching the surface. These are two rather enormous questions.