Chemical Sharpening

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Feb 28, 2009
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Greetings all!

I spent a little time on the road yesterday and the craziest thing popped into my soon to be senility laden head. Does anyone or has anyone tried to chemically sharpen a knife blade? Fishook manufacturers do it. Drop your old worn files into a vinegar bath for a couple of days and say "Make it so #1", the next thing you know your files are usable again. Does this process transfer to our beloved blades successfully? What say ye?
 
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Feb 10, 2014
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Greetings all!

I spent a little time on the road yesterday and the craziest thing popped into my soon to be senility laden head. Does anyone or has anyone tried to chemically sharpen a knife blade? Fishook manufacturers do it. Drop your old worn files into a vinegar bath for a couple of days and say "Make it so #1", the next thing you know your files are usable again. Does this process transfer to our beloved blades successfully? What say ye?
How would you get the chemicals to corrode or eat only the metal you want off and have it stop at a sharp, straight apex?
 
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Well, first are you saying "files" or "flies"? You are talking about fishooks, then, whammo, files.

Second, I suppose getting oxidation off your edge might "sharpen" it, but beyond that the idea doesn't make sense really. How would you use a chemical to remove steel symmetrically and smoothly from the edge of a blade?
 
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Ive seen chemical sharpening on files before. But I dont think it would transfer over to a knife in the sense of what we call sharp. The reason it works for a file, to my understanding, is that most of the time the file is "pinned." Pinning is when the teeth on a file are clogged with tiny pins, or metal shavings. When you chemically treat it, the chemical you use eats away at the metal clogging it. For aluminum its especially bad. It'll gall to the surface or weld if you will. "Cleaning" it will help release the bond of the metal clogging it while etching the teeth. So instead of a shiny smooth surface, its now rough again. It'll sort of square up the teeth again to where they cut. Leaving a dull to dark grey surface similar to Ferric chloride on Damascus steels. Im terrible at explaining sciency things. Think of rust on a car. Its jaggged and sharp where it started as a smooth metal body panel. You're forcing a controlled erosion on the steel so no iron oxides form and turn to rust. While corroding your blade edge could make it somewhat sharp by removing material, it would also be bad for the edge too. Forming or turning the edge into oxides making it brittle. Causing faster wear and damage that needs ground out. Files dont thin out to an apex but instead have stepped ridges and or small raised flats with gullets between that grab and remove material so this isn't a problem. If you use hydrochloric acid you will have a bad time as well. You may run into whats called hydrogen embrittlement, where hydrogen is introduced into alloying elements causing extreme brittleness, cracks, and breaks.

Now I could be completely wrong as well and you have stumbled upon the next great sharpening system. This is all based on half cracked research and learnings over time with no real end goal other than to answer a question I had at the time. Id take it with a bucket of salt or at least a few grains.
 
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Folks in Aerospace facilities could do some pretty neat stuff by dipping objects in acid. They would obviously control all the factors obsessively like an aerospace engineer would. There were coatings that would be used to protect where you didn't want the acid.

There were a lot of weird and crazy hobby things produced off hours. The company at the time encourage the staff to do this; I'd suspect it kept the folks sharp and while you were making super light RC car wheels maybe you'd find a new better way to make something for the planes too.

I don't' know if you could get a knife as sharp as on stones or belts this way. Even if you got par I think the time investment and hazard with the chemicals would be a deal breaker.
 
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But man I can just imagine the late night commercials.

Sharpener in a Can; spray on your garden tools and rinse with with water 5 minutes later. Chop down trees with it all day and then slice tomatoes for dinner with it after.

Better than that screen door boat.
 
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The way the chemical sharpener for flies and files sounds like it deep cleans it. I imagine an ultrasonic cleaner would be just as effective or more, and quite a bit quicker too.

To sharpen a knife by chemicals would require a lot of money, precision engineering, and acids to get it all just right. And even than I'm not entirely convinced we possess the ability to make it as sharp as what some of us can do it with just a stone. It would also require a precision set of measurements of the blade, knowing exactly what it is made of, heat treat etc. It's not really feesable.
 
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Bench: My thoughts have centered around using the acid bath as a final step in the sharpening process to refine the edge of the "micro-bevels". By using etch resistant masking material everywhere you do not want the acid to react with the blade material the etching process could be limited to the actual edge. The area exposed to the acid bath may only be .010"-.060" perhaps a little more.

Marcinek: I would think linear agitation of the blade may help.

Swoop03: Worry not, I followed that. In the past I have done my best to clean my files and rasps before the acid bath. Next time I do a batch I think I will have to take some close-up photographs of the before and after examples and compare them. Of course, it wouldn't have to be limited to an acid bath as alkaloids are corrosive as well. Or perhaps Hydrogen gas? I am sure the grains of salt I have taken over the years is now in the buckets range by now.

Danke42: A place I once worked promoted the after hours experiments on home projects , too. It was a fun time. The chemicals and what to do with them when you are done with them is always a problem ... kind of like spent nuclear rods. Sharpener in a Can, I think we better get our agents working on the right spokesman immediately!

Bob6794: I suspect it is not economically feasable as well. But my curiosity has me wondering if anyone has tried it.

We used to have a fellow here in town that had more wild & crazy ideas than one man should be allowed ... his name was George Leonard Herter and if you are old enough you to remember George you know he was World Famous. I, however am not and I do not intend to be.

 
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FortyTwoBlades

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Chemical sharpening works on files for a number of reasons, one of them being that while a file is a sharp tool it's not sharp in the same way that a knife is sharp. The etching process with files does do more than just unclogging them, but it wouldn't produce comparable results in a tool like a knife whatsoever.
 

Lesknife

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There’s also a chemical reaction to metals known as acid embrittlement. I don’t know what the ph level would have to be to cause embrittlement but I believe for files it isn’t a concern as they are brittle to begin with where as I wouldn’t want to make my knife brittle.
 

StrangeDaze

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There’s also a chemical reaction to metals known as acid embrittlement. I don’t know what the ph level would have to be to cause embrittlement but I believe for files it isn’t a concern as they are brittle to begin with where as I wouldn’t want to make my knife brittle.
Does that mean forcing a patina with vinegar or something similar could make your knife more brittle? Would it be the whole knife or just the very edge?
 

Lesknife

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Does that mean forcing a patina with vinegar or something similar could make your knife more brittle? Would it be the whole knife or just the very edge?
Most store bought vinegar is a 5% solution that is used to force a patina and usually for a short time to only affect the surface of the blade and then neutralized by a plain water rinse and then oiled . I believe it would have to be a higher acid percentage for a long soak for the acid to penetrate though the metal to embrittle it and depending on the alloy.
 
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miso2

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I've heard a myth that some Japanese natural stones chemically affect the edge during sharpening, thereby providing finer finishes than what expected from the apparent grit sizes.
 
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