Hamon Types

[Bryce]

G'day Guys,

Can anyone tell me how different hamon types are produced? I am not thinking of the shape of the hamon, but specifically why did Gassan Sadakatsu produce a hamon with a very thick nioiguchi, while Yokoyama Sukenaga produced a thin hamon like a laser beam? I know that a thick nioiguchi is generally regarded as desirable, but why? What characteristics do each of these hamon types impart to the steel? Below is a photo comparing a Gassan Sadakatsu hamon to one by Bizen Sukenaga.

Cheers,

Bryce

[Bryce]

These are what the blades look like under direct light. Sadakatsu on left and Sukenaga on right. The Sadakatsu has much finer nie (konie) than the Sukenaga.

Cheers,

Bryce

 

[DTM72]

I may be wrong but it believe it has to do with the insulating properties of the clay, and how it was applied. Just my opinion, if the clay thickness had a transition in thickness from the ji area towards the ha, (think of an angle from thick to thin) then the result would be a wider nioiguchi. Conversely, if there was more of an abrupt change in the thickness, (think of a step) the result would be more of a narrow or sharply defined nioiguchi. The whole point of the clay is to insulate the upper portion of the blade to pervent it from hardening during yaki ire. The clay in the ha area is very thin and can even be a different compound than the clay in the upper area. To me it is easy to imagine the differences of hardening between the two thicknesses of clay...but what about that are where the two meet? That is where the magic comes in and different schools teach what to make the clay from, how to apply it and in what style, not to mention the temperature of the quenching water, how long to hold it in there on the initial quench, then the reheating and tempering of the blade after initial yaki ire. Your question may be best answered by an actual blacksmith who has performed this process and obtained the differing results you see above.

Again, I may be totally wrong, but at least I am willing to offer a theory, and get the ball rolling.

 

Someone correct me or prove me wrong! I'm always willing to learn.

 

Dan

[OceanoNox]

If you want to see how cooling changes the phases present in the steel, then a TTT diagram (Time-Temperature-Transformation, or isothermal transformation diagram) is the way to go.

https://en.wikipedia.org/wiki/File:TTT_diagram-20201210-isothermal_transformations_in_steels.svg

 

On such a diagram, all areas of the blade would start at the same temperature, ideally, but the clay would make the cooling rate different. To read the diagram, take a point at your starting temperature (top left), and draw a straight line going downwards and to the right, with a slope corresponding to the cooling rate (i.e. clay thickness). Quenching in water with thin or no clay would be close to vertical (typically 1~2 seconds).

 

As you increase the clay thickness, you get martensite that becomes mixed with bainite, pearlite, and ferrite in increasing amounts (for the thickest clay zone, there should be no martensite).

 

In terms of mechanical properties, stress concentrations are not good, so a flamboyant hamon might not be the best, and I have read that suguha was the best for a reliable blade, but I cannot recall who said it (possibly Takano Sasaburo, or at least a famous practitioner of tameshigiri).

Edited April 19, 2023 by OceanoNox
Spacing for better readability

[Bryce]

Thanks guys,

When you look at the huge differences that can be achieved using water as the quenching agent, I imagine that a similar range of results may be possible using oil as the quenching agent? Where I am going with this is that in the military swords forum a common question is "is this an oil quenched blade?" Some blades are obviously oil quenched, some blades are obviously water quenched, but I bet there are many blades where it is impossible to know with certainty, what quenching medium was used?

Cheers,

Bryce

[David Flynn]

Bryce, I think you're trying to compare, apples with oranges.   When one has seen many, many showato, spotting an oil tempered blade becomes  easy.

 

[OceanoNox]

8 hours ago, Bryce said:

When you look at the huge differences that can be achieved using water as the quenching agent, I imagine that a similar range of results may be possible using oil as the quenching agent?

Oil quenches are more gentle on the metal, especially if the oil is heated up (depending on the steel, martensite can form as high as 200℃, so you can quench in 200℃ oil, and then slowly cool down to room temperature, and you will get a fully martensitic piece without risk of cracking). Oil quenching would probably give less sharp lines between the phases (but I have not seen any myself).

The polish is what will tell you the difference. It is not clear how the blades looked like before, but a sax was polished by a Japanese polisher and it showed a hamon (https://www.archaeologie-online.de/artikel/2001/thema-alamannen/mado-wo-akeru-ein-fenster-oeffnen/).