Ruined edges on leatherwork knives?

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ScottEnglish

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Apr 11, 2020
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Hi. I paid someone this morning to grind some English style paring knives back to their original shape. I had altered the shape by hand on a Crystolon stone. The result was not an improvement over the original shape as I had hoped. Not wanting to spend a lot of time grinding them back to their original shape, I paid a professional to do it for me.

The three knives are now back in my possession. However, each of them has a band of colour, which is mainly blue, about an 1/8" to 1/4" in width running along the length of the edge on the non-bevel side. Has the temper been ruined?

Thanks.

Scott
 
ScottEnglish said:
Hi. I paid someone this morning to grind some English style paring knives back to their original shape. I had altered the shape by hand on a Crystolon stone. The result was not an improvement over the original shape as I had hoped. Not wanting to spend a lot of time grinding them back to their original shape, I paid a professional to do it for me.

The three knives are now back in my possession. However, each of them has a band of colour, which is mainly blue, about an 1/8" to 1/4" in width running along the length of the edge on the non-bevel side. Has the temper been ruined?

Thanks.

Scott
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The are definitely softer at the edge, they may still be usable but they will need sharpened more regularly. Personally I’d be contacting the “professional” and requesting a refund at the least if not replacements depending on how expensive the knives are.
 
Yeah your blades were definitely overheated. The “professional” should have known to keep the blade as cool as possible while grinding to avoid this. I wouldn’t necessarily say they are ruined, but if you use them frequently, you will probably notice a difference in edge retention.
 
ScottEnglish said:
Hi. I paid someone this morning to grind some English style paring knives back to their original shape. I had altered the shape by hand on a Crystolon stone. The result was not an improvement over the original shape as I had hoped. Not wanting to spend a lot of time grinding them back to their original shape, I paid a professional to do it for me.

The three knives are now back in my possession. However, each of them has a band of colour, which is mainly blue, about an 1/8" to 1/4" in width running along the length of the edge on the non-bevel side. Has the temper been ruined?

Thanks.

Scott
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Yes. They're in the ball park of saw temper now if they were a relatively plain steel to start with (O1, A2). If you use them in leather, the edges will roll - and if the leather has silica, faster and worse.
 
Thanks for the replies.

The only camera I have is on my laptop and the photos I took of the knives were very poor and not worth adding.

If I grind off, using my stones, the band of colour, will the remaining steel have kept its temper? Thanks.

Scott
 
It's going to take too long to remove the band of colour on my stones so I will buy replacement knives. Thanks for saving me wasting time on them.

Scott
 
ScottEnglish said:
It's going to take too long to remove the band of colour on my stones so I will buy replacement knives. Thanks for saving me wasting time on them.

Scott
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the answer to your question is yes - if you can regrind the blued portion of the steel (or reharden and temper if doable), what's left should be OK.

what you can't tell is if the last temperature marking is the only one as the blue is just a surface coloring and you can literally polish it off without much effort.

Not uncommon for the blued area to be "good enough" part of the way in, but in woodworking where grinding tools is a routine part of sharpening, beginners (who have no discretion) are told to grind off the blued area.

Bummer that they have to be discarded.
 
While I agree it's a botched job, this fact has been discussed MANY times.

Color of steel oxides during/after heating is not a reliable indicator of temperature or temper.
 
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ScottEnglish said:
Thanks for the replies.

The only camera I have is on my laptop and the photos I took of the knives were very poor and not worth adding.

If I grind off, using my stones, the band of colour, will the remaining steel have kept its temper? Thanks.

Scott
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Yeah thats why I was wanting the pics to see if the knives could be reground/reshaped into something still useful for skiving, (paring on east side of the pond, skiving here).
 
Keith Nix said:
While I agree it's a botched job, this fact has been discussed MANY times.

Color of steel oxides during/after heating is not a reliable indicator of temperature or temper.
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Can you point me to these discussions? When the color occurs quickly while grinding, it's a decent sign. When time is involved, at least from what I've seen, then color in an instant and color of the same temperature over time will not match.

Never hurts to try something that's been blued to see if it is only shallow or not that significant.
 
Just search for flame tempering, torch tempering or some such
 
Got it - I see what you're talking about. Thanks for pointing me to it.

If the colors are ground through to the back side of a knife, though, or straight into it grinding it down, they should be pretty reliable (overheating through the thickness). But I'd always try something (including tools), sharpening and use - before throwing it out. Not clear from above if these were tried.
 
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