Here's a video of the successful smelting furnace in action. This technology was unquestionably the biggest barrier in the process. Once I had a fire hot enough to smelt copper, I was able to make iron in a couple extra days. The tiny little pocket of fire is about focus, I think- focusing the energy of charcoal and air to reach a temperature not found ordinarily in nature- in fact, probably the hottest sustained spot anywhere up to the radius between me and an industrial plant, a temperature beyond the scale of anything domestic or wild, probably only found naturally in magma and lightning. Creating these yellow fires, a transformative circumstance that doesn't exist ordinarily, gave humans a leverage: we could create materials that had different properties than the things lying around us. I would like to convey that this is a really, really, powerful feeling. It made me feel like I could do anything. Of course, in the end, I came down from this buzz somewhat, once I realized I spent 6 weeks developing a skill set that was useless outside of the game I set up for myself. There is no reason for me to continue honing my metal age metallurgy; the experiment has only been useful in offering perspective, for myself and hopefully others.