Black spot during hamon etching

[leeskeeee]

Hello,
So I am doing a hybrid etching to bring out the hamon on a white 2 honyaki. Where the hamon ends, there is a black/dark spot that forms from one side through to the back side. I dip my cloth into my etchant and wipe both sides going back and forth and don’t let the enchant sit for long before another wipe/coat. Does anyone know what that mark is and what it means? It’s at the end where the hamon line stops. You can also see the dark spot on the spine of the knife in the same area.
Thanks!

 

[MSicardCutlery]

Could be an inconsistency in your cleaning method. Could be some unevenness in the carbon content of the steel (but I doubt it). I'd be curious to know it it remains after polishing with loose abrasive.

 

[leeskeeee]

Could be an inconsistency in your cleaning method. Could be some unevenness in the carbon content of the steel (but I doubt it). I'd be curious to know it it remains after polishing with loose abrasive.

For cleaning, I washed with dish soap, dried, wiped with isopropanol alcohol, rinsed with water, then dried.

 

[Lurkernomore]

That’s where they do extra tempering to prevent cracks. Normally the namiukashi will fade out toward the spine to hide that but if you do full surface etching or blasting the safety temper spot will show.

 

[leeskeeee]

That’s where they do extra tempering to prevent cracks. Normally the namiukashi will fade out toward the spine to hide that but if you do full surface etching or blasting the safety temper spot will show.

ahhhhh that makes a lot of sense. Thank you for that knowledge!

 

[Lurkernomore]

BTW the same thing happened with the blue one gyuto group buy knives. Same smith, Togashi, but everyone does it the same way. As far as I’ve seen it’s done by pinching the area with red hot tongs but there may be other ways.

 

[Kippington]

BTW the same thing happened with the blue one gyuto group buy knives. Same smith, Togashi, but everyone does it the same way. As far as I’ve seen it’s done by pinching the area with red hot tongs but there may be other ways.

I had totally forgotten about this method. I recognized it as an over-tempered spot in the picture, but I couldn't work out how it got there hahaha

If anyone is interested, it is done to prevent cracking where the hamon contracts and the hardened steel expands. I've learned this through experience

 

[aporigine]

I had totally forgotten about this method. I recognized it as an over-tempered spot in the picture, but I couldn't work out how it got there hahaha

If anyone is interested, it is done to prevent cracking where the hamon contracts and the hardened steel expands. I've learned this through experience

Props for the drawings. Terse elegant communication.