by Jason Crawford · April 15, 2017 · 2 min read
Did you just spell “melting” wrong, with an extra letter? No, smelting is the process of extracting a metal from its ore.
Before I started this project I had a very vague notion of what ancient smelting was like. I pictured it something like this: “ore” is like a rock with some little bits of metal mixed in. You make a bonfire and you hold the rock over the fire with, like, tongs or something. The rock heats up and the metal in it melts and drips out, leaving… a rock with holes in it, like Swiss cheese. Maybe you hold a pan under it to catch the dripping metal.
Smelting is nothing like this:
Ore is not a mixture of rock and metal. The metal itself is often oxidized. So you’re not just separating metal and rock, you actually need a chemical transformation to strip away the oxygen.
You don’t heat the ore over the fire. You actually dump the ore and the fuel together into the furnace and ignite the entire mess. The molten metal drips down. In some furnaces it collects in the bottom in a “bloom”, a blob of hot metal that you pull out with tongs. In other furnaces (hotter ones, I presume), liquid metal runs out and down channels into molds.
There are often other substances involved too, including some that play a role called “flux”; I’m still fuzzy on this but it’s something like a catalyst. And there are other substances that come out of the furnace, including “slag”, which I think is the impurities that are separated out of the ore.
Here’s a good YouTube video showing the smelting process:
And here’s another showing smelting and then forging of the resulting bloom:
Some observations from watching this and the charcoal video:
All this stuff is a lot of work. The videos only show snippets, but you can tell that each process takes hours and hours of hard physical labor. And the result in the end is unimpressive by modern standards. Watch the end of that last video: Hours of pounding a piece of metal with a hammer, reheating it, and pounding it some more, and you end up with… something that is finally, recognizably “a piece of metal”. It’s not even useful for anything yet.
At every stage of the process, there is no guidance and no guarantee of success. Does this dirt contain iron ore? Not sure… it looks kind of red, so maybe. Is the fire hot enough? Not sure… oops, we didn’t get a good bloom, maybe not. You can go through the whole smelting process and just end up with a piece of slag. You could make a charcoal pile and come back days later only to find that you didn’t burn it correctly and your wood didn’t char properly.
Social media link image credit: Morgan Riley, CC BY-SA 3.0
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