One of my (many) interests is metallurgy. Specifically, the history of it, known as archeometallurgy. I was interested in it all those years ago when I studied anthropology and archeology in school, and then I married a guy who did inspections on chunks of metal all day. So living with the husbeast has expanded the knowledge quite a lot, and he and the guys he works with are always surprised at how much I know. They of course know far more than I do from a practical viewpoint, but I know more about the history of it. We have many interesting talks.
This summary is REALLY general, because many metal-working methods were invented in different parts of the world, at different times. (Plus we don't wanna be here all day.) Skills were also dictated by what was available in the area. Please keep that in mind when reading it. Not all cultures worked neatly through the list; many skipped the silver and gold phases. Many more stalled at other stages, unable to invent the needed technology to work other metals. Some, like Australian Aborigines, walked around on top of very large iron deposits, but lacked the knowledge to use them, lacking the other, softer metals to experiment and learn on, first.
It is generally accepted that cultures who independently developed metal working did it by working from softer, more obvious metals to harder metals that need more specialized skills. Copper, gold, and silver are the metals that most cultures started with. That's because it's possible to pick up (or dig up) chunks of it that are nearly pure, that can be hammered into shape. From there, humans worked up to alloys and smelting and casting and all that good stuff.
That's a chunk, there, straight out of the ground. You can see how it's possible to pick up a bit and mash it into what you want, from there with a handy rock. It is the most malleable and least reactive of metals, certainly of the easily-found metals. Since gold like this is fairly pure, and therefore soft, it's thought that most early gold pieces were decorative. Probably, making gold decorations was a natural offshoot of using pretty rocks for the same reason.
This is a Scythian piece, the arm of a throne, from the 7th century BCE. You can see by then goldsmithing was very sophisticated. Gold has been worked for at least six thousand years; I suspect longer. It's very hard, nearly impossible, to date metal unless it is found with some kind of organic material. I also wonder how many of these pieces were melted down and re-worked a couple times before we found them.
Silver is a bit more reactive than gold (tarnish? that's silver mixing with oxygen and sulfur in the air), and therefore a little harder to find in pure form, but not much. Otherwise, its history is much like gold. It is also very easily worked, with a low melting point (961.78 °C, 1763.2 °F, lower than gold). The meltability of gold and silver may be what gave people the idea for casting and smelting, which would come in handy later on when fooling with copper, bronze, and iron.
This is the Gundestrup Cauldron, one of the most famous pieces of ancient silver working in the world. It was found in a Danish peat bog and is thought to date from the first century BCE. Because it is more common than gold, it was worked more extensively around the world. Because it corrodes, no one's quite sure how long we've worked it, but everyone agrees it's thousands of years. Silver is one of the best conductors of electricity, and is used widely in industry for that purpose. It is also used in photographic film and x-ray film. Until huge deposits of silver were found in South America, devaluing the currency, Europe ran on a silver standard. After that, they switched to a gold standard.
This is where things started to get tricky, and the human race had to improvise. Copper does this thing called 'work hardening'. When you hammer it, it gets much harder and more brittle. After a while, you can't hammer it into shape; it breaks. Heating it can soften it and make it workable again. I suspect ancient smiths stuck copper in a fire, and noticed it got runny, and thought 'maybe I could pour that into this hole...' and casting was born - if they hadn't done it with silver already. Copper is the first metal that advanced metallurgy was used on (that we know of).
This is a decoration made by the Hopewell culture in North America, sometime between 100BCE and 500CE (near where I grew up). It is said copper working goes back ten thousand years in the Middle East. While I don't dispute that, I wonder whether it was truly the first metal worked; it's more common than gold or silver, so it was the first metal worked in a widespread manner, therefore leaving more artifacts behind to be found. Could be gold and silver working are just as old, and we haven't found evidence of it yet. From a technical standpoint, it is definitely possible.
This copper axe was found with the body of Otzi in Europe. The accurate dating of it (to 3300BCE) re-wrote the history of copper working in the area. So, yeah, I doubt we've found everything there is to find yet.
Bronze is a collective term used to describe an alloy - two or more metals mixed together - containing copper. In the ancient world, it was most often mixed with tin or arsenic. It was rather clever. Copper tools showed people the possibilities for metal tools and weapons, but copper is really soft. What made it so easy to learn on, made it lousy for any kind of item intended for hard use. So people started melting it together with other stuff, that made it harder. Tin was apparently the preferred choice, but it isn't nearly as easy to find as copper. Some of the world's oldest trade routes carried tin from Europe to the rest of the world. Bronze working is officially dated from 3000BCE.
This is a Shag Dynasty bronze vessel, from sometime between 1600BCE and 1000BCE. The Shang were arguably the best bronze casters in the world. Their technical expertise impresses metallurgists even now.
IRON: (last one!)
Iron is great for tools because it's hard. Unfortunately that makes it difficult to work. It also has a pretty high melting point (1538 °C, 2800 °F), which is hard to achieve with a wood fire, which made smelting it tricky. The human race had to kind of work up to it, using all they learned working other metals to make iron useful. It is thought the Chinese used porcelain-making techniques (porcelain has a very high firing temperature) to figure out how to work iron, which they had a lot more of than they had copper or tin. As with the others, I'm not sure the dating is correct because of how easily iron corrodes (rust), but it is officially dated to 1300BCE, first worked in the Middle East and then spreading outward as others learned the techniques needed. Iron triggered the first arms race in history; groups like the Hittites, armed with iron weapons, went out and whipped up on civilizations that were still using bronze. The war between the Hittites and Egyptians resulted in the world's first known peace treaty, a copy of which hangs in the United Nations right now.
Didn't know metallurgy was quite so interesting, did you?