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more wootz [Apr. 5th, 2011|11:41 am]
Doug Ayen
On Saturday, I remelted the wootz ingot as had been suggested at the hammer-in by people more experienced in wootz-mongering. Pretty simple: I put some powdered charcoal in the bottom, along with a bit of graphite (I have bulk graphite as a parting-powder for the casting setup), put the larger chunk of wootz in the crucible, covered with borax, glass, and fluorite flux, and fired up the furnace.

Since I was using a smaller crucible, I decided to try to fit in a 2nd one, this one containing a mix of flux, magnetite, and charcoal powder similar to what I had seen at the hammer in. This is called a carbothermic smelt, or crucible smelt.

After running the furnace for a couple of hours, the wootz was liquid, and the crucible smelt was . . . interetsting. Poking the wootz with an iron rod, I could tell that a bunch of stuff was still on the bottom of the crucible, with the iron floating on top, itself topped by a layer of flux. I gave it a good stir, scraping the bottom, which at 3000F took a bit of precaution and work. The crucible smelt was semi-liquid, and I couldn't really get a good feel for how it was doing. I gave it another half hour to let things settle, and killed the furnace.

On Sunday, I pulled the crucibles. One side effect of putting both in, side-by-side, was that the crucibles were fused to both the base block and the wall of the furnace, and getting them loose damaged both crucibles to the point that they couldn't be reused. The wootz cake came out pretty clean, with some evidence of carbide formation on the top, and only a small amount of leftover charcoal/graphite in the bottom of the crucible.

Since the estimates by the experts at the hammer-in were that this was fairly low carbon, I had added in the extra carbon sources in the hopes of raising the carbon content to ~1.5% -- although it's hard to say with this sort of process how well that worked out, the spark test shows that it at least has significantly more carbon now. I just hope it didn't absorb too much and turn in to cast iron. Some quick hits with a hammer shows it's pretty malleable, though, so I'm hopeful.

The crucible smelt, though, failed pretty much completely. In the crucible was a black, porous mass, with some bits of iron in the matrix, but clearly it had not finished smelting out the iron -- hitting the mass with a hammer to judge it's consistency sent sparks flying. I'm guessing I didn't let it run long enough, and will try again using this material as well as additional ore and charcoal.

Forging wootz is something I've never done, but from the hints I got at the hammer-in, the first step is to normalize the cake a couple of times. I discovered that this ingot is too big to fit in my propane forge, so I've re-heated it now a couple of times in the furnace -- not too efficient, but it gets the job done. I'll adjust the Little Giant to handle the extra thickness and try to draw it out next, working at an orange heat and moderate blows to prevent cracking/falling apart. Whee.

[User Picture]From: dcseain
2011-04-05 06:48 pm (UTC)
Most interesting. Thanks for sharing.

A great-uncle of mine used to work at the GE Newark Quartz Plant, making quartz crucibles for the steel industry. He brought home ones with faults, which got used as pots for plants.
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[User Picture]From: blackanvil
2011-04-05 06:50 pm (UTC)
Yeah, I'm using cheap clay-graphite crucibles, but quartz would be very, very cool. And probably very, very expensive.
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