How much polishing is too much?

[Pie]

Let’s say I polish a knife many times. For the sake of quantifying, 10 times. Each time a 3 or 4 stone progression starting from 400 grit to 8k, or coarse/medium/fine. Keep in mind I’m not entirely sure what I’m doing, but keeping the pressure moderate and trying not to spend more time than necessary on the lower grits. Maybe spending a lot of time on higher grit.

Of course, in the process of polishing, steel will be removed. This is cannot be denied. The question is this “too much” steel being removed for little more than aesthetics and amusement? I guess a better question is, would polishing a knife over and over result in enough steel removed to negatively impact performance, or is it actually an insignificant amount?

I do realize it is entirely dependant on each individual’s polishing process, but I’d like to hear what you guys think.

 

[Luftmensch]

7 times....


the answer is 7 times....

 

[Luftmensch]

I kid.

No... if you very literally mean polishing, you are removing extremely small amounts of metal. It is hard to see how that could perceptibly affect geometry. It will be insignificant. However, by changing the surface finish you may induce different amounts of stiction.

If you mean serious refinishing (as you implied) to remove heavy scratches, the answer is still "unlikely" (in my opinion). You could eventually damage things like kanji or makers marks. That may happen after a handful of serious surface refinishes.... It depends on the etching/depth etc... but blade geometry? No... i still don't think so. The limit will be really high (you won't have that much patience ).

Routine thinning in the course of maintenance does far more 'damage' to a knife. Of course, you aren't really 'damaging' the knife - it is part of maintaining performance. But thinning will be the fastest normal cause of removing metal. For most mere mortals, the impact this will have on longevity is small and is a slowly occurring process.

 

[Benuser]

My question would rather be: what do you aim for with all that polishing? If you want to remove deep scratches you have to start by the grit that caused them. Otherwise all further work will be vain.
Polishing beyond a certain medium grit will affect negatively food release.
As for the aesthetics: a polished surface is more vulnerable.
It's my understanding considerations may be very different with single-bevelled in Japanese cuisine. My own experience is limited to double-bevelled in Western cuisine.

 

[TB_London]

I reckon you could rub a knife on and 8k stone for 24 hours straight and lose a few mm tops.

what you’re doing could be done hundreds of times and not cause any real issue. Unless you have a target you’re aiming for it’s likely to be unproductive though.
Get a wide bevel knife and work on getting those big bevels even, consistent, and polished. You’ll learn more and be able to see what’s happening better

 

[ian]

You can certainly change the geometry of a knife if you spend hours on a 400 grit stone.

 

[RDalman]

impact performance.

What is performance?

 

[ian]

Thinner is always better.

 

[Nemo]

Stop polishing the knife when you can see through it.

Seriously though... what @Luftmensch said.

"Polishing" is the removal of very small amounts of metal, mostly with fine abrasives. The idea is to impart a particular surface finish (e.g.: Kasumi, mirror).

"Thinning" is the removal of a fair bit more (or even heaps more) metal (often with coarser abrasives), aiming to optimise the cutting performance by creating an geometry appropriate for cutting. This can be anything from:
1) The removal of a little metal just behind the edge to counteract the gradual thickening behind the edge that occurs during sharpening (maintenance thinning)
2) Removal of a lot of metal behind the edge if the edge has gotten very thick due to a lot of sharpening without maintenance thinning (restorative thinning).
3) Taking a new knife that is too thick behind the edge and thinning it out (corrective thinning). The actual process is similar to (2).
4) Removal of metal further up the blade face to maintain/ restore/ correct the entire blade geometry. This requires an understanding of the geometry that you are aiming for as well as how to achieve this geometry with the tools that you have available.

 

[tostadas]

If you've ever tried thinning by hand, you'll realize that it takes forever to remove a significant amount of steel. And that's when you're actually trying to remove steel. If you're only messing with the surface finish, it will take even longer to remove significant amount of steel. Also, I dont think you will be dropping down to 400, or even 1000 grit often if your intention is for refinishing a polish.

 

[big_adventure]

I spent a couple of hours thinning an iron clad nakiri on a SG220 stone. It ate about half of the stone, and severely dished it. The knife was only thinned 0.2mm 1cm behind the edge and it only lost 4g of weight. Polishing a knife, with fine stones, fine paper, or compounds win't remove any appreciable amount of steel.

 

[Nemo]

I spent a couple of hours thinning an iron clad nakiri on a SG220 stone. It ate about half of the stone, and severely dished it. The knife was only thinned 0.2mm 1cm behind the edge and it only lost 4g of weight.

Yeah, I like coarse (120ish grit) sandpaper if I'm doing this much work. I reckon a belt grinder would work great too.

 

[Pie]

Thank you all for your input. Since I’m not even close to using thinning pressure, time or stones, I’m going to worry less about messing up the geometry of the knife.

Basically what is happening is I polish, it doesn’t look amazing, I do it again with the higher grit stones, use the knife once, get some weird patina, and restart the cycle. Sometimes it doesn’t even make it to the knife using step. Really I’m looking for reassurance I’m not going to &%@#$ up the makers grind by spending a bunch of time screwing around with the finish, looks like I’ve found the answer .

Much appreciated

 

[Jovidah]

Just take note of what Benuser said; polishing too much might look pretty but it's actually going to be more sticky and the food release will get worse. I'm not sure where the sweetspot is, but 'mirror polish' is definitly beyond it...

 

[ian]

Basically what is happening is I polish, it doesn’t look amazing, I do it again with the higher grit stones, use the knife once, get some weird patina, and restart the cycle. Sometimes it doesn’t even make it to the knife using step. Really I’m looking for reassurance I’m not going to &%@#$ up the makers grind by spending a bunch of time screwing around with the finish, looks like I’ve found the answer .

Hah, seems like you just like polishing? Although note that there are ways to remove patina without changing the finish much. Use some metal polish like flitz or something.

If you post some pics of your polish jobs, perhaps people could give you advice on how to get where you want with it.

 

[Pie]

Just take note of what Benuser said; polishing too much might look pretty but it's actually going to be more sticky and the food release will get worse. I'm not sure where the sweetspot is, but 'mirror polish' is definitly beyond it...

Duly noted. As a home cook I’m not overly concerned about the stiction, I haven’t had a case where it’s actually become a problem. 99% of the time I’m looking to achieve a kasumi finish of varying smoothness, the core is the only part that really ends up getting close to mirror.

@ian That seems to be the case lol. Some nights I just want to mess with the stones but sharpening = losing (small, but significant) height whereas polishing = low impact entertainment. Lack of experience and inconsistency really seems to be the glaring issue. For example, I polished the heck out of one side of my practice knife last night on a jnat, switched to the other side without new slurry and was wondering why the core steel was so much brighter. Lesson learned - old mashed up mud isn’t going to do the same job as new crunchy slurry when it’s not a synthetic. I’ll check back in 10 years or so .

 

[btbyrd]

Any polishing is too much polishing. I only care how it cuts.



Your mileage may vary.

 

[VICTOR J CREAZZI]

Over polishing isn't really a problem as it really simple to un do. For the premium matte finishes the recommended sequence it to go to mirror and then apply the matte with new coarser (600 grit) abrasive.

 

[big_adventure]

Yeah, I like coarse (120ish grit) sandpaper if I'm doing this much work. I reckon a belt grinder would work great too.

Yup, sandpaper's what I typically use as well, but I wanted to use stones only for this job. Here I was just trying to give the example with numbers to let the OP know that he doesn't really have to worry about changing geometry with polishing.

 

[Pie]

I spent a couple of hours thinning an iron clad nakiri on a SG220 stone. It ate about half of the stone, and severely dished it. The knife was only thinned 0.2mm 1cm behind the edge and it only lost 4g of weight. Polishing a knife, with fine stones, fine paper, or compounds win't remove any appreciable amount of steel.

This mirrors my experience with thinning. It’s damn hard work if you’ve got to do “corrective” thinning. I’ve bunged up a few because I got bored and lost focus.

also thank you @VICTOR J CREAZZI , will give it a shot going all the way and then stepping down to lower grit.

Current polish mule - it’s lost roughly 10mm height and I’ve thinned the crap out of it so it’s nice and flat for practice.

 

[Luftmensch]

it’s lost roughly 10mm height and I’ve thinned the crap out of it so it’s nice and flat for practice.

Stop the press! Is that a typo? You lost 1cm during thinning? That sounds awfully excessive!

 

[Pie]

Stop the press! Is that a typo? You lost 1cm during thinning? That sounds awfully excessive!

Oh no it wasn’t me, I bought it like this. Used to be a moritaka kiritsuke 240 demo knife at the local shop, purchased just to dip my toes into jknives. I’ve had it a good 4 years now. It’s lost maybe <1mm by my own hand mainly to flatten and clean up the profile.

THIS is the new polish mule. I probably won’t live long enough to lose significant height on this one.

 

[stringer]

Just to give you some perspective. When I was at my peak production in pro kitchens, sharpening a couple times of week I went through about 1-2mm a year in knife height rarely going lower (or higher) than 2k for my most used and abused gyutos. Always thinning the entire bevel geometry a little at a time. (So something in between thinning and polishing) Probably 5 minutes a session 100 times a year. so 500 minutes a year. That's a lot of hours of sharpening to cut through very little steel.

 

[inferno]

imo you will lose almost nothing when polishing a blade side. the knife will most likely last for 10-20 years even if its your only knife.

 

[Luftmensch]

Oh no it wasn’t me, I bought it like this. Used to be a moritaka kiritsuke 240 demo knife at the local shop

Nice one @Pie!

To me... there is less exposed core material than I would expect. This could imply a 'fat' primary bevel. Perhaps in the past, too much pressure was applied to the edge during thinning (as opposed to the shinogi/shoulder)? Or maybe somebody removed a chip the easy way?? I am not familiar with Moritaka knives, so I dont know what the factory grind is like... but I would prefer to see a higher weld line on a san-mai knife.

Should you choose to do any further thinning, *I* would put all the pressure at the shinogi line. Try to push the weld line up towards the spine so that you have a thinner knife behind the edge. If you do this perfectly, you can shave the shoulders down without losing blade height. In reality you will lose some fraction of a millimetre! But that is my preference!!! If you are happy with the way it cuts, my observation/preference is moot

Either way; looking good! You have a nice low-mid grit finish there!!

 

[ModRQC]

Starting like JIS 600 and up, steel removal is inconsequential: you're painting more than removing material.

JIS 300 - 600: significant steel removal will take hours.

JIS <300: significant steel removal will take 30 minutes - 1 hour. Nose ballpark, I'd say such a session tends to remove about 1g of steel.

Significant steel removal= 0.1-0.2mm on a wide surface.

The closer you get to the edge, the more "significant" such a small amount becomes. Also, while little steel actually, it can dramatically change the geometry of a knife, depending WHERE the efforts are applied.

 

[Pie]

Lots of great insight, thank you guys.

Nice one @Pie!

To me... there is less exposed core material than I would expect. This could imply a 'fat' primary bevel. Perhaps in the past, too much pressure was applied to the edge during thinning (as opposed to the shinogi/shoulder)? Or maybe somebody removed a chip the easy way?? I am not familiar with Moritaka knives, so I dont know what the factory grind is like... but I would prefer to see a higher weld line on a san-mai knife.

Should you choose to do any further thinning, *I* would put all the pressure at the shinogi line. Try to push the weld line up towards the spine so that you have a thinner knife behind the edge. If you do this perfectly, you can shave the shoulders down without losing blade height. In reality you will lose some fraction of a millimetre! But that is my preference!!! If you are happy with the way it cuts, my observation/preference is moot

Either way; looking good! You have a nice low-mid grit finish there!!

I agree, in some places the cladding is very close to the edge, but hours of thinning gave almost imperceptible results. Moritaka knives theoretically have an angled blade face, resulting a shorter primary bevel but by this point in its life it’s no longer exactly how the maker wanted it. I do need the practice easing shoulders and shaping in general, it’ll be a good long term project. Thank you for the suggestion!

 

[Mikeltee]

I buy knives for use in the kitchen. I spent a lot of money on them therefor looks are irrelevant as long as I can scream through product. Polishing removes metal and takes life out of the knife. I'm sure I would change my attitude if I owned a $1000 blade, but I don't, and I don't see myself ever spending that. My $300 blades do what I need them to do. Are they better than my $50 blades? Yes... would a $1000 blade be better than my $300 blade? I doubt it. Would it look better? Absolutely!

 

[ModRQC]

Hmmmm... polishing basically is a corollary of thinning, which is a corollary of sharpening, which is a corollary of using a knife. It thus restores life to a knife that's getting thick and doesn't zip through food anymore. Most of the polishing done doesn't remove steel so much, it basically just "paints" it. If looks are irrelevant, then polishing you can avoid to some extent. The activities that actually remove significant steel are unavoidable though. And up to a certain point, you'll need to polish the scratches left from thinning or food separation will take a dire hit.

 

[Benuser]

Sure, but there is quite a gap between removing the scratches from thinning and polishing. No reason for going beyond 2-3k.