The following was posted by Lee Sauder on to Facebook. As frequent readers here know, Lee is largely responsible for the Early Iron movement in the USA (and a close friend). I have stolen his posting to the 'Iron Smelters of the World' Facebook group to help spread his suggestion.
Since Mark (Green) brought up the twist testing, I thought I'd you tell my way of doing it. I've been testing blooms this way for a couple of years- the nice thing about it is that you not only get the subjective feeling of the iron, (which is easily confused or forgotten), but there's an easily quantifiable record as well-- how many twists it takes before it fails. I've found this very helpful to understand what I've done without expensive chemical analysis, which isn't really as meaningful as how tough the iron really is. I like do do this with the bloom hot right out of the smelt, so the test is still connected with the memory of the smelt.
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| Sectioned bloom and ancony with twist test. |
If we all did this in a similar way, we'd have a better way to compare and communicate our results. Here's my way- could I propose this as a standard to communicate with?
I originally did both hot twist tests and cold twist tests, but now I usually just do the cold twist test, which seems to tell us the most. I forge the bloom to a bar approximately 5/16 inch ( 8 mm) square, (with no folding). Let it air cool. I mark off 1.5 inches ( 38 or 40 mm), and twist it until it breaks, counting the quarter turns.
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| Close up of twist test |
My low-carbon, high phosphorus blooms break at zero to 1/2 twist, with a crystalline fracture. The low-C, low P blooms go 3/4 to 2 twists- the best we've done so far did 2 full twists, the one shown in the photos.
Ductile fracture at 2 complete twist.
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| Crystalline fracture at 1/4 twist. |
The hot twist tests I do by forging to 5/8 inch square, marking off 3 inches. heating to yellow. and twisting to failure. The higher P ones actually tend to twist farther hot than the low P ones. Usually in the neighborhood of 3 to 4 twists before it breaks.
I actually have never done this with high C bloom, so I don't know how it acts.
I think this is a great way to judge your iron in your own shop.
The images and text above all by Lee Sauder
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