We went out to Spokane to build a furnace. I'm only posting this picture because I love the area, love the way the scent of sage gets into your hair and everything you touch, basalt crystallized into six-sided columns, stars bright and clear and true as the ring of an anvil, and the way the heat pulls against your skin. The ground is written differently there, the marks of fire and flood and ice, cryoturbation and erosion and metamorphosis.
How to build a furnace:
First, dig a hole.
You want rocks to line the hole with. Ideally, they should be rocks that don't melt, crack, shatter, or metamorphose in the heat. Let me know if you turn up any; I've had no such luck. We used a landscaping rock called 'Montana Red,' which appears to be landscaper-speak for 'kind of reddish sandstone'. We broke it into large sheets and lined the pit with it.
The rock had sheets of mica in it, which was a neat effect. The mica has different thermal properties than the sandstone, and glowed more brightly, so that when the rocks were in the pit and the furnace was burning, you could see the sheets of mica laid through them like a shining skeleton.
You need some refectory. This is insulation; it reflects heat back into the furnace. Certain types of clays are traditional, but we used powdered basalt left over from digging a well. It was a bit glassy and holographic; if you leaned over so your shadow fell on the pile of basalt dust, you got the distinct impression your shadow was in the wrong place by a few centimeters.
The furnace right after ignition. Actual charcoal (as opposed to processed and chemically-enhanced briquettes) is hard to find, so we ended up purchasing gourmet mesquite charcoal, scented sharp and smoky. At one point, I spilled soda across the stones, and it carmelized instantly, cracklesharp and sweet-smelling, like creme brulee. There was also a sharp subtle hot-metal scent, familiar to anyone who's worked in a machine shop. I would not have predicted that smelting would smell so wonderful.
Ore mixed with iron oxide for flux. The general idea here is that the iron is supposed to combine with the silica in the copper ore to make a compound with a much lower melting point. We mixed it with our hands, and then wandered around being red-handed zombies for a while. They we tried to wash it off. Then we resigned ourselves to being red-handed zombies for the rest of the day. I think I finally got the last of the ochre off my hands nearly a week later.
It makes very good cave paintings, though. :) I hope future archeologists wonder why there's a cave painting of an armadillo in a tophat in Eastern Washington.
This was a reducing fire - that is, we worked very hard not to let extra oxygen into the pit to steal our copper away into copper oxide. Using charcoal instead of wood helps, since charcoal is pure carbon and grabs any extra oxygen that happens to wander into its territory for carbon dioxide. Covering the pit also helps. A strange thing about the reducing fire is that the sparks did not come out of the fire itself, they appeared suddenly about a foot above it where they could get oxygen. From a distance, it looked like the fire was hovering ghostly over the ground with no apparent fuel source.
Making marshmellows over a furnace is a moral obligation. Luckily, we are all good, upright, ethical citizens. Note some cave painting in the background.
All magic is fire, I wrote once in a story I was too embarrassed to post. :) But everything we touch has a hidden color that only fire can find, a light that cannot be seen without unmaking. I wish I was good enough with a camera to show all the little rivulets and puddles of color in smeltfire - dyes from paper used as kindling, blue and red, and little tongues of copper-green like snakescales, edged in gold, and a strange pale yellow like sunset through water.
That was a lot of heat. The red-brown rocks cracked crosswise into thin layers, translucent and pale as paper, laid into unbound books the shape of a hole in the ground. They were strange colors, blue grey purple white, and crumbled into knife-edged shards as we were digging at them, so thin you could see the heat of your fingertips through them.
Glass we made, too, in bubbles and bumps, mostly jet black, but shot with gold and green and copper, and heavier than glass should be.
The strangest things were the dream-butterflies, thin sheets of translucent white marble, sketched in copper and greengold glass by vapor deposition, stuck askew in pairs and chains and jagged DNA-spirals by shimmering black. Fragile and impossible, like three-dimensional calligraphy, or the weight of flight.
Dissected butterfly wings, marble and copper and greengold glass.