Break Test for Wrought Iron

A simple test for wrought iron is to cut partway through a bar and then break off the rest. It will bend and then finally break, revealing stringy iron fibers rather than the homogeneous matte-gray internal structure of modern steel. The linear striations are caused by the residual slag left between layers during smelting and refining and are often appreciated as an aesthetic point in artistic works.

Wrought iron is a fairly pure form of iron which was manufactured for all structural and utilitarian applications prior to the modern advent of mild steel. Production declined steeply around 1890 when mild steel largely replaced iron for structural applications, though production for specialty and restoration work continued on a smaller scale up into the 1960s. It is usually easy to identify in the wild by the way it corrodes into a wood grain like appearance rather than the moon-textured look of corroded steel.

Island Blacksmith: Charcoal forged knives from antique steel.
This rail plate came from a railway that was abandoned before 1926 and is made from wrought iron over a century old.
Island Blacksmith: Charcoal forged knives from antique steel.
A break test can confirm wrought iron or layering as well as indicate the level of carbon in a piece of scrap.
Island Blacksmith: Charcoal forged knives from antique steel.
The way the layers bend and break shows a finely layered wrought iron texture.
Island Blacksmith: Charcoal forged nihontou made from reclaimed and natural materials using traditional techniques
A beautiful example of the linear wood grain appearance of the surface of highly corroded wrought iron.
Island Blacksmith: Charcoal forged nihontou made from reclaimed and natural materials using traditional techniques
By contrast, highly corroded steel exhibits a pitted or cratered erosion surface pattern.
Island Blacksmith: Charcoal forged nihontou made from reclaimed and natural materials using traditional techniques
Positive results of a break test for wrought iron (in some cases this test might also indicate annealed or mid to low carbon shear steel and a hardening break test should also be performed).
Island Blacksmith: Charcoal forged nihontou made from reclaimed and natural materials using traditional techniques
Note the stringy, layered structures that are revealed as the ductile iron fibers bend and eventually give way.

Forging wrought iron should be done at a much higher temperature than high carbon steel or even mild steel. At lower temperatures there is an increased risk of cracking along the slag lines whereas higher temperatures ensure that everything is in a malleable state. Punching and drifting must be done with care and at very high heat, resist the urge to keep forging into the lower range as it cools. Because wrought iron contains almost no carbon it can be safely heated to a bright yellow or almost white heat without burning up. In terms of planning and shaping, the grain direction of the layers must be considered, almost as if working with wood.


Island Blacksmith: Charcoal forged knives from antique steel.
The unusually shaped piece of rail plate from the break test above…
Island Blacksmith: Charcoal forged knives from antique steel.
..shaped into the form of a yoroidoshi tanto using only hammer work.

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