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What are the rules for etching steels?


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A bit of a broad question.

I want to know more about what different etching agents do to different types of steel(mainly speaking of low and high carbon steel)

 

So ferric chloride turns the hard steel dark and leaves the soft steel alone 

What I was looking for tho was the opposite.

 

So I don't know jack.

and I'm back to square one.

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All etchants will etch more on hard steel than soft steel, because the hard steel is in a more energetic state than the soft. The final look is dependent on what you do after the etch - polishing out the oxides, buffing, boiling, blueing etc. What are you trying to do?

 

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I'm trying to go for the Japanese blade/tool finish.

Soft steel black

Hard steel white

 

There has to be a way to do that without using stones.

 

what about damascus then?

That has steel that doesn't turn black and it would be insane if that was a non-hardening steel, that would make for a terrible blade with lots of little soft spots 

 

 

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For damascus these days most people use a high-nickel steel like 15n20, L6, or 8670 for the bright line, so there's no problem with differing hardness.  In the old days (as in 1980-2000) we used pure nickel foil or A203E for the bright layers, and that did indeed result in a blade with hard and soft spots (for the pure nickel) or a lower carbon than anticipated (with the A203E).  We didn't care.  It was still pretty, and that's what we were after. 

 

For Japanese-style hamon, a lot of what you are seeing is due to lighting.  If you use a reflection of a black background in the blade, you do get a bright edge and dark spine.  In person, a full traditional polish is fairly subtle.  The little etching that is done is done mostly above the hardened edge to bring out the microstructure.  It's not a dip-and-forget kind of etch.    

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Yeh I had heard something about nickel steels.

 

So there is no magic etching or staining stuff, (other than cold blue) that can bring out a dark coloration in the low carbon steel?

 

I could a sworn some of the stuff I'd seen was etched, but maybe it was a stone polish with accommodating lighting...

 

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On 11/28/2020 at 6:01 PM, J.Leon_Szesny said:

Yeh I had heard something about nickel steels.

 

So there is no magic etching or staining stuff, (other than cold blue) that can bring out a dark coloration in the low carbon steel?

 

I could a sworn some of the stuff I'd seen was etched, but maybe it was a stone polish with accommodating lighting...

 

 

As far as I know the black colour on soft steel in japanese swords is indeed a reflection, in jewelry and clockmaking this is called a ''black polish'' if something is really flat and high polished it will turn black when not reflecting a light source directly.

 

I remember reading somewhere that the fullers and spine of japanese swords are often burnished with a steel, this creates the final super glossy finish.

Burnishing actually isn't hard to to, just very very time consuming.

 

If you are trying to get color contrast in a san mai, I would go for a nickel steel core and manganese steel sides, after etching in ferric this will give dark sides and a bright edge.

In my experience etching normal mild steel will just give you an unattractive grey.

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