Oroshigane steel (5)..... using the sumihira style furnace

The Sumihira style furnace has been completed and drying for a few days…..it's time to take this bad boy out for a spin.

Remember that stubborn little stick of mild steel that we just couldn't melt, using the “Aristotle” furnace? Reverting back to the dread air mattress inflator makes reducing this iron into a blob of unrecognizable goo a breeze ( no pun intended... really!).

Starting out, flames are thin and red in color, with just a hint of blue at the base of the flame ( which you can't see here because the sun is too intense in Hawaii).

As the furnace comes up to melting temperature, the flame becomes much “thicker” and shifts towards a more orange color.

You also get a good view of my ghetto style blower motor, duct tape and all.

Knowing when to pull the molten bloom from the hearth is going to take me a bit of time and effort to get dialed in. Sumihira writes that as the process nears completion, the intensity of the flame will moderate some and also shift into the yellow spectrum. Then…..you turn off the noisy blower and listen. The molten steel will sound as if it's boiling.

If you think that it is about ready to come out, let the charcoal burn down until it reaches the tuyere, then turn off the air, grab a tool to hook out the bloom and…..

…..see what you got.

Looks like a burnt-iron cookie!

Another thing that I've been wondering about…...water quenching the bloom. In the handful of resources devoted to small scale iron smelting, YouTube, etc, when the raw bloom gets pulled from the furnace, the consolidation work begins immediately. The yellow-hot blob of steel is thrown onto a log or anvil, then gets gently pummeled by guys swinging sledgehammers. This squishes the odd protruding edges of the bloom into the concentrated center, consolidating the mass. The goal is to get the slag and other impurities out of the way as quickly as possible, resulting in a tight block of bloom iron or hearth steel.

In contrast to this, pretty much all of the Japanese resources on tatara ( the traditional large scale way to make steel) and Oroshigane show the hot bloom pulled from the fire and then immediately quenched into water. The bloom gets cleaned up, then returned to the forge for shaping and consolidation. Why would you not start working the bloom right away while it's still good and hot? Does the force of the water quenching blast off the slag and bits of charcoal stuck to the bloom?

Here's my chance to find out.

Fun, lots of boiling water and funny noises are produced, but as far as the resulting bloom is concerned, I'm not sure that the quenching does anything to tidy up the mass.

Rather ugly, this one.

I've seen lots of pictures of bloom steel and while this wouldn't be the ideally shaped result, it does display a commonly seen dished profile.

In this picture, the air blast would've been coming from the left. Please excuse the green strings of algae growing in my quench water, haha.

This entire process, from preheating the furnace to pulling the bloom from the fire used less than half of a 5 gallon bucket of hardwood charcoal, not a bad way to spend an afternoon. Even if you buy your charcoal in the store, that's still only a few bucks cost, a good deal even for a tightwad like myself.

The nice thing about performing an immediate water quench is that it makes the bloom available for spark testing right away. I sparked this little 1 lb. bloom but, try though I might, I couldn't get any decent pics as the sun was just too bright. Ahh…. the trials of living out in the open, haha. I'm grossly out of practice at interpreting carbon values by spark, but it looked to be a gradient of med/high carbon ( shortish yellow spark with strong bursts) ranging up to cast iron (very short red spark, sparse). A few bits tested low carbon, but the highest proportion looked to be cast iron.

This bloom would most likely be forgeable, given a high enough heat and a bit of patience. Fold and weld, fold and weld, and soon you would get a more homogeneous steel…….and I didn't do that. The melting of iron was so much fun that I immediately started in on a second melt, just to see if I could create a bloom with a more solid core. And larger, in anticipation of losing much of the total during the welding and blending phase.

One thing is certain though…..I need to be keeping better notes. Small changes in procedure seem to have large ramifications on the resulting steel. Go figure.