Yakiba and Fukura difference from Omote & Ura sides

[MHC]

Hello all,

 

First off let me state that I have really no opportunity to view swords in person, as the availability in Thailand is scarce. So I'm relegated to photos online and in books, as my information source {I know, I know not ideal to say the least}.

 

Looking at various photos of Tantos, I often see a stark difference on the temper line detail from side to side. Several tantos I've seen pictured, barely even display any distinguishable temper line on the Omote side, while the Ura side is very clear even showing partial or entire return temper on the Mune.

Is this simply a style of clay prep before tempering via individual smiths, or is this a sign of many polishes, thus removing enough metal on one side , diminishing the original detail?

 

Second question relating to all swords, does showing core steel after a swords polish, negate it's value, or is it simply showing that the sword is on its final polish?

 

Thank you in advance for helping out a fledgling rookie.

 

Mark

[John C]

2 hours ago, MHC said:

negate it's value,

Mark

I imagine this is a matter of preference. According to this source, it's a sign of a "tired" blade. I would think that age, rarity, and smith play a larger part in value. But some may consider it a deal breaker.

John C.

[Jacques]

There is no shingane on tanto (too small). 

[Brian]

There very much can be. I know it's said tanto didn't use kawagane and shingane, but there is no doubt that some tanto were made that way, and I have a late koto/early Shinto tanto showing shingtetsu after many polishes. I have zero doubt some smiths did make tanto the same way they made wakizashi and katana. We already had this debate way back: https://www.militaria.co.za/nmb/topic/49145-shintetsu-good-bad-or-acceptable/

http://www.ksky.ne.jp/~sumie99/shingane.html

 

[Jacques]

2 hours ago, Brian said:

There very much can be. I know it's said tanto didn't use kawagane and shingane, but there is no doubt that some tanto were made that way, and I have a late koto/early Shinto tanto showing shingtetsu after many polishes. I have zero doubt some smiths did make tanto the same way they made wakizashi and katana. We already had this debate way back: https://www.militaria.co.za/nmb/topic/49145-shintetsu-good-bad-or-acceptable/

http://www.ksky.ne.jp/~sumie99/shingane.html

 

Reliable sources please

[CSM101]

Minamoto Masao

 

I hope, you can see it.

[Lewis B]

Interesting.

[CSM101]

You had the chance to handle the blade in Berlin. 

[ROKUJURO]

3 hours ago, Jacques said:

Reliable sources please

And for your statement Jacques.

[ROKUJURO]

On 10/1/2025 at 3:55 AM, MHC said:

.....Looking at various photos of Tantos, I often see a stark difference on the temper line detail from side to side. Several tantos I've seen pictured, barely even display any distinguishable temper line....

Is this simply a style of clay prep before tempering via individual smiths.....

Mark,

there is no clay application for the tempering (= YAKIMODOSHI). This is only done before hardening (= YAKIIRE). What you call "temper line" is in fact the hardening line (= HAMON).

Generally, clay application is mostly done with one side of the blade at a time (there are videos on that on YouTube). In this case the HAMON may not be symmetrical on both sides. However, some smiths took great care in producing almost "mirrored" HAMON.

Japanese nouns do not have a plural form, so it is always TANTO (not Tantos)

[Bazza]

I have seen shingane in a Kotou tanto with my own eyes...

 

BaZZa.

[Jacques]

On 10/2/2025 at 8:50 PM, CSM101 said:

Minamoto Masao

 

I hope, you can see it.

What makes you say it's shingane? And what does shingane look like?

[CSM101]

Occam's razor: what is it?

 

I created a dark spot with Photoshop to fool everybody

Rai hada

Sumi hada

Tekkogane

Shingane

 

Choose wisely.

[Rivkin]

Can't fool me. Its chikei.

[MHC]

On 10/3/2025 at 4:44 AM, ROKUJURO said:

Generally, clay application is mostly done with one side of the blade at a time (there are videos on that on YouTube). In this case the HAMON may not be symmetrical on both sides. However, some smiths took great care in producing almost "mirrored" HAMON.

All information regarding traditional hardening (Yakiire) of the Hamon, clearly state this process is done complete (entire blade), and only once. The clay compound is applied to the entire blade, both sides, only one time. This is a very critical step in the process, with some swords not surviving the process. These failed swords may require re-work or disposal.

 

Additionally, sorry for my use of the word "temper", that was incorrect on my part. Still learning the correct terminology for use regarding Japanese swords.

 

Mark

[nulldevice]

Yoshihara Yoshindo mentions that a well made blade can be hardened several times if the original quench doesn’t produce desirable results.

 

He says this is done by heating the blade to a yellow color and letting it air cool to soften the blade and then re-coating it in clay another round of yaki-ire. 
 

 

[MHC]

Yes Chandler that is true, as you stated, after softening the steel, the entire blade can again be coated with clay and repeat Yakiire. Very risky however, as each repeated attempt may result in a compromised blade.

 

The point I was referring to, was that each side of the blade cannot be hardened independently, as mentioned previously by Jean. It is done all at once, no other method is possible.

 

Mark

 

[ROKUJURO]

Mark, Chandler,

this is a complete misunderstanding!

Clay-coating of a blade (= TSUCHI OKI) is usually done one side after the other prior to quenching - I did not say 'hardening' was done side after side! I tried to explain why a HAMON usually is not perfectly symmetrical on both sides.

Re-hardening (= SAI HA) can indeed be done, but as a side-effect, long blades can show a stronger SORI afterwards because of the martendsite expansion.

Repeated hardening also results in a material loss as some superdial steel is oxidized into scale.

Of course there is no "softening" (or normalizing) of the steel necessaray prior to a second hardening unless the blade has to be worked on, e.g. straightening it. Heating it up to yellow heat (= 1.150°C) would not only damage the blade but also be useless as the hardening is completely gone already at 750°C.

 

[nulldevice]

46 minutes ago, ROKUJURO said:

Of course there is no "softening" (or normalizing) of the steel necessaray prior to a second hardening unless the blade has to be worked on, e.g. straightening it. Heating it up to yellow heat (= 1.150°C) would not only damage the blade but also be useless as the hardening is completely gone already at 750°C.

 

I hope I wasn't implying blades are hardened 1 time per side. I was rather referring to Yoshindo's book where he said if a smith is not satisfied with the results of the hardening process, one can reheat a blade to remove the temper and then start again. Now in his book he mentions heating the blade until it is golden yellow and allowing it to air cool to soften the steel before restarting the clay application, heating, and quenching for a 2nd time. 

 

[ROKUJURO]

Chandler,

I understood your post completely. This may be YOSHINDO-SENSEI's way to do it, but as I wrote, technically, it is not necessary to "soften" the steel for a new hardening process. It is not a "better" way, but causes scaling.

[nulldevice]

Just now, ROKUJURO said:

Chandler,

I understood your post completely. This may be YOSHINDO-SENSEI's way to do it, but as I wrote, technically, it is not necessary to "soften" the steel for a new hardening process. It is not a "better" way, but causes scaling.

That's valid. I don't pretend to know what temperatures or procedures are best. I'd love to read other detailed accounts of how sai-ha and other re-hardenings are performed. Especially if there are any records from Yasutsugu and the likes who retempered many famous blades that had been damaged in fires.