How To Tips for hamon line interaction with bluing

[Hawaidy1]

Hey there! Recently a friend commisioned me to make a knife with a hamon line, however he also wanted me to blue it. Will a hamon line persist after bluing or would i need to re-harden the blade? Would bluing it before hardening the blade work as well?

 

[Stacy E. Apelt - Bladesmith]

The two things -bluing and hamon - are not normally combined. They are sort of opposite effects.

Depending on the method of bluing, the hamon should be fine, but the color will cover up some of the details.

You can't blue a blade and them harden it.

What is normally done is to etch the blade in FCl and then hand polish out the lower bevel (ha) to meet the hamon. Cold bluing would work similarly. Hot bluing is not usually suitable for blades, as it affects the temper.

 

[Tyson A Wright]

Hot bluing is not usually suitable for blades, as it affects the temper

How does this wreck the temper? I was under the impression that most hot bluing setups were under 300° F, which should be below temps that damage temper, right? Nitre bluing runs much hotter- more like 650° F (which is why it's usually used for screws and pins in firearms but not for frames and barrels). Curious to learn more about hot bluing knives- thanks!

 

[Richard338]

Kyle Royer hot blues lots of parts at about 270F, achieving a very black look on mild steel. I wouldn't be as worried about the temper as I would the overall look trying to keep a hamon.
I wouldn't want to try this for the first time on a commission.
I suspect what the customer actually had in mind is more like a San Mai with a bright nickel line combined with the bluing.

 

[Stacy E. Apelt - Bladesmith]

Yes, I was thinking of some other higher temperature methods that use higher temps. Niter salt bluing is done at 570F. Boiling baths are lower and should be safe for the temper.

 

[navasky]

Hot bluing I don't know about, but I can tell you that slow rust bluing makes the hamon completely disappear.