SCA 50 Bloomery Smelt a la Wareham Forge

It was my great good fortune to attend the SCA 50 year celebration, and while I was there I spent a fair amount of time hanging out (and occasionally helping out) at the "Bloomery Iron Smelt" experiment that Darrell Markewitz ran.

It was the first time I'd ever actually been at the forge when the bloom was extracted, and I have to say I was pretty overwhelmed. I had to leave early Wednesday morning, so I'm not sure how the into-the-night reheat or next-morning compaction went, but I was glad to be there nonetheless.

Here's a short video showing some of what we did:

Hope you enjoy.

Think like an engineer: Cheat!

Faced with several smelting failures, I decided to apply one of the sacred tenets of practical engineering taught to me by my father: "When it won't work, cheat". I swapped out the clay forge for one made of loose-stacked firebricks, solving my spalling and insulation problems at a single blow. I was confident charcoal with forced air could get me the temperature I needed if I got a working geometry for the forge. Here's what I ended up with:

[edit post to add picture here]

Additionally a more knowledgeable copper smelter from the other side of the Atlantic Ocean, gave me some good advice about how to test for what was going wrong. (Thank you Fergus!) Armed with this information, and general his encouragement, I took another shot.

On Wednesday, 16 Jun, 2010, I completed my first copper smelt. Here's a short (and very self-important) video of the results.

I plan to do another smelt tomorrow, on a slightly larger scale, so I'll take pictures and video, and post them.

Past efforts: Smelt 2, partial success

I wanted to compare the various containers, so I tried some open to the flame (cast iron servers, 1 terracotta cup) and some closed (2 clamshelled cups, 2 stacked ramekins)

I put them in the bottom of the forge, and piled in the charcoal.

Each container had a mix of large chunks of broken malachite and ground charcoal. I lit the fire and started a'blowin. I reloaded the fuel several times, eventually using the entire bag of charcoal. Once the entire thing had burned down to a bit of ash and a few glowing coals, I extracted the various containers. The cast iron server looked like this. (the circle on the right is the open terracotta saucer)

Safety tip: beware hidden coals... as I started to empty this (by hand, the cast iron was cool enough to touch) I found this guy hiding in the ash...

Ipicked out the larger chunks more gingerly, and ended up with the same result: a lot of ash-looking stuff, and no pooled copper in the bottom of any of the containers. Then I started noticing a terracotta-colored brittle substance at the bottom of each of the containers. It was fragile and brittle, but not charcoal, and it was present in all the containers, so it wasn't shards of pottery.

I decided that it must be partly red copper oxide (Cu₂O) encased in black copper oxide (CuO), which looked a lot like little chunks of charcoal. This meant that I'd partially reduced the malachite, but didn't actually get to a liquid copper state.

But now I was faced with a problem: I had copper oxide chunks and charcoal that both looked like small black brittle lumps. How could I separate them? After spending 5 minutes teasing them apart and sorting them visually (the charcoal always had striations in the surface) the "idea" light over my head started glowing weakly. Carbon floats, ash is partly soluble, and copper oxides are insoluble. Enter the sophisticated scientific apparatus known as "a glass of water":

After fishing out the charcoal lumps from the froth, and draining and refilling the glass several times (being careful not to tip out any copper from the bottom) I ended up with the copper oxide "lode" at the bottom of the glass. The black lumps are not charcoal nibs, they're black-jacketed copper oxide.

Remembering my leftover "ash" from smelt #1, I emptied that into the glass as well. Presto, more copper. I hadn't made it vanish after all.





I emptied them onto a paper grocery bag to dry:


After examining them for a bit, and comping to the conclusion that the problem had been a overabundance of oxygen, I decided the next step was to put the oxides back into the forge, heat it up, and do my best to make sure that the fire was hot enough to reduce the oxide, and make sure that there was a dearth of oxygen in the containers.

Side note: The Revol ceramics unsurprisingly didn't hold up. Apparently it was too hot for them: the glaze on one cracked, and the other actually broke in the fire, presumably from exceeding its design parameters by 800-900 degrees. :)


Onward to smelt #3!

Past efforts: Smelt 1, making copper vanish

In the morning, with the forge *cough* chiminea *cough* set up, charcoal and blowpipe at the ready, I set up a small pile of lump charcoal, inserted the cone with some of the dust, and lit the coals. Using the blowpipe took a little practice, and I couldn't keep a 100% duty cycle for the hour-plus it took for the charcoal to burn down, but it did seem to make a difference. Still before noon, the charcoal had burned away, and left ash and assorted rubbish in the bottom of the chiminea. The cone had tipped a bit, so I wasn't too shocked when it didn't contain a little lump of copper at the bottom. I carefully shoveled out all the ash, and started sifting through it. The problem was, I didn't really know what I was looking for: I expected to find a little solidified button or puddle of copper, either on the bottom of the forge or in the cone. Nope. Clearly I was a more powerful alchemist than I had realized: I had caused the substance to disappear entirely! :)

I assumed that the copper had done one of two things: broken down into prills so small I didn't recognize them, or literally floated away in the breeze as either vapor or very hot micro-prills. Nevertheless, I set aside all the ash from the bottom of the forge and kept it for later.