Smelting Results

[gfish]

This weekend vixyish, corivax, shadowblue and I went to visit my parents in Spokane and smelt some copper. It was a filthy, tedious, exhausting, fabulous project, and it even kind of worked.



Crushing the ore


Crushed ore mixed with iron oxide for flux.


Caught red-handed!


The furnaces were simple holes in the ground, with 1 inch black iron pipe for tuyeres.


It was lined with stone and packed with powdered granite for insulation.


Rock slabs provided a lid. Wonderfully primitive.

It was preheated with charcoal for an hour, then we started adding ore/flux. It was fired for another 5 hours after that.


It made for excellent marshmallow roasting.


After letting it cool, we searched the ashes. We ended up with a small collection of actual, vitrified slag. None of them contained copper.


First furnace with the lid removed, letting it burn down. You can see the bright spots around each tuyere.


We decided the first was far too wide, and built the second like a narrow cylinder, so that the hotspots would overlap and allow for a nice head of charcoal to burn down into the bottom.


Second furnace burning. The blower is electric, with a nice adjustable speed controller. (Not very authentic, but who wants to spend 6 hours pumping on goat skin bag-bellows?) On the second firing we decided to worry more about getting a hot fire than keeping the conditions inside reducing. This seems to have been a good decision.


Second furnace being opened up. The rocks were not a very good choice, and crumbled with the heat. This dropped fragments into the furnace. We added more iron oxide to counter the extra silica this was adding, but it looks like we didn't add enough. Next time we need to find something more like sandstone, which the rock yard didn't have. Agricola was right -- hard rocks don't stand up to the heat very well.


The entire bottom of the furnace was a large chunk of slag. Much better than the spotty little bits from the first run.


Large lump of slag. Most of it was real slag -- glassy iron silicates -- but there were large inclusions of bits of rock from the lining.


And this is what we got. The stuff on the top is all slag and random bits of nicely marblized lining rock. The small chunk below is actual metallic copper, maybe enough for 2 or 3 BBs. We crushed almost all the slag looking for bits that deformed instead of shattered, and this was it. There were also some hints of metallic copper deposited as very thin layers. The current theory is that the ore we used was just too poor for these very primitive extraction techniques.

So there it is. Two days of very hard work for less than a gram of copper. But I'd sure love to do it again. Next time I'm going to shell out for a kilogram or two of malachite for ore. And we're going to use sandstone, possibly with a fired-clay furnace. The great thing is, this could be done in our backyard. It was really very low impact and very contained, for being a fire that was reaching somewhere around 1000 C.


I'm going to write this up as a complete website with lots of pictures and details soon. I'll post a link when that is up.

Comments

[randomdreams.livejournal.com]

I was also going to suggest some sort of refractory. If you're intent on doing everything by hand, that's a bit more difficult, but if you're willing to buy fire clay and mix it with some sand and broken up stone, you'll have a wonderful firepit that should last through anything you can throw at it.

It's my understanding that the ancients used rock chimneys up the side of steep mountains, to get a natural draft-blast, for large-scale refining, rather than goat-skin bags, but that's way larger-scale than what you're looking at.

I'm incredibly envious.

[gfish.livejournal.com]

I'd really like to do it just once using a completely traditional design. But I've already been thinking about simple designs for a freestanding little furnace, using modern refactory materials. It sure would be fun to move on to tin (and, therefore, the bronze age) after getting copper down. The chalcolithic was a bit of a lame duck. It would be nice to get firmly into a more interesting age.

(A few years ago I outlined an idea for a cyberpunk hobby of people working their way up the tech-tree of global civilization. At the time I thought I was doing it for background material for a story, but now I'm thinking it was more of a life goal. And I can't even fall back on my standard excuse of developing useful post-apocalyptic skills.)