Might be the difference in steels used and repeated polishing play a role in this feeling. As per Sugita Yoshiaki's excellent work certainly it is needed to watch very close and attently to get the difference between the two ways of hardening. Present days Togishi makes wonders.
As per the genesis of hadaka yaki might be this have some interest to you :
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However, some blades seem to have experienced repeated re-tempering such as the Warabite-tô excavated in Negishi, Kurihara district, Miyagi Prefecture in the possession of Mr. Matsumori Meishin, City of Tsukidate in Miyagi Pre-fecture or the example excavated in Iwate Prefecture (exact place of excavation unknown), in Masakuni„s possession, or the so-called „Maigusa-tachi“ (nagasa 77,3 cm, sori 2,5 cm), Kanagawa Prefecture. In old documents on swords Masakuni found out that additional measures to increase the hardness of a cutting edge – that means not only by applying a yakiba – were applied to softer steels. This is described by the term “uzumi-yaki“ , which means to fire an ob-ject by inserting it completely in hot ash. This might suggest that with this additional measure, eventually warabiteto were heated by sinking them entirely in hot ashes of the cooled charcoal fire. It Seems to be the description of a re-hardening at lower temperatures, around 400° C. Six Form I warabite-tô from the Tôhoku area up to Hokkaidô were polished, and each of them was hardened with uzumi-yaki. Among such swords in uzumi-yaki, there are examples with an extremely soft hitatsura-like yakiba, and also pieces in which it seems that the kissaki area was re-tempered. All of these blades don´t show a hamon the way we know it, but rather a strong utsuri. All this might suggest the swords were hardened without (or with poor) clay cover, and that the difference in hardening between the mune and the ha is due only or mainly in the difference in cooling rate caused by the different thickness of the blade. It is possible that this process later evolved in the one that some present day Tosho suggest is at the origins of Kamakura Choji Hamon achieved without clay but with better steel, better smithing skilfullness and higher temperatures.
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