Thinning and polishing: What did I do wrong? What did I do right? A feedback thread.

[OkayMode]

I am a competent sharpener, but have very little experience thinning and polishing - something I am trying to change.

After failing to sell it, I decided to use my Manaka Shiro #2 Bunka as a practice knife. The cladding was reaching up to the edge in a few spots and has fairly flat bevels thanks to Manaka’s process, so this seemed like a good opportunity to make it more enjoyable to use and practice my technique.

I did most of the thinning with a Naniwa 1k, applying pressure evenly across the bevel at first from the edge up to the shinogi, identifying the low spots in the process.

I was able to mostly grind the low spots out by applying pressure at the edge and then moving the pressure upwards to reduce and eventually remove it, although I didn’t try to pursue it excessively with one or two particularly stubborn bits.

Similarly, I was able to push the cladding line back along most of the knife edge, but there are two spots which after a decent amount of effort refused to budge much. I decided to stop when the edge became nail flexing thin.

If you look at how uneven the hira is between both sides, I think the grind might just be a bit wonky, which makes sense as I bought this knife a little while ago when Manaka was less experienced and sought after than he is now.

After getting to a nail flexing edge along the majority of the blade save the heel, I decided I was broadly happy with the thinning job and stopped for the day.

Today I figured I would have my first ever go polishing, starting with a Morihei 500 and removing most of the really ugly stray scratches before moving on to an Imanishi 1k, getting the scratch pattern consistent, and finishing on a Morihei 3k.

I thought building up a slurry was meant to help develop an even finish, but I found if I let it build up, I would check my work and find a HUGE lone scratch requiring an additional 5 mins of buffing out - what’s that about?!

I decided I was happy enough with the finish on the stones when the core steel had developed a clean polish and the kireha had a nice enough kasumi with a consistent scratch pattern. There were definitely lots of deeper scratches I hadn’t worked out, but I know perfection requires a lot of time, effort and skill, so no dramas.

At this point I though ‘eff it, let’s get the Flitz and stone powder out to see if it helps cover up the low spots until I eventually work them out properly.’

I applied Flitz first with a cotton pad which pulled back the contrast on the kasumi significantly, but gave it a more consistent texture. It ruined my nice mirror polish on the core steel though, so I probably wont be doing that again.

I then used the stone powder, which returned a bit of contrast to the kasumi (although not as much as it had off the stones), and returned a bit of the polish to the core steel but nowhere near where it was before. The end result was less contrasty than off the stones, but better blended overall in my opinion.

I am happy enough with the result for someone very new to this, but am confident there are loads of things to improve - I just don’t know exactly what, and how to fix it!

Any and all feedback on what I need to improve and develop on is welcome, please point out any mess ups too!

Pictures show the before, video shows after.



Thanks for reading

 

[tostadas]

Did you grind too much and remove the cladding to reveal the core in those areas?

 

[KasumiJLA]

Did you grind too much and remove the cladding to reveal the core in those areas?

That was my thought too! I never saw a cladding that thin to be shown off only by removing low spots?

@Ok__mode_6953 I think you did a good job especially if you’re not doing it often. That’s the learning process!

But I would start with something coarser than a 1K stone, especially if you have low spots. It’s gonna be way faster and you will save a bit of your 1K stone too.

You could have saved your mirrored core by only applied your stone powder directly on the jigane if it was mirror finish or used some finger stones which can makes a nice finish.

Don’t give up! Polishing is fun but there’s a learning curve of course

 

[OkayMode]

Did you grind too much and remove the cladding to reveal the core in those areas?

You mean the areas up by the shinogi on the right hand side by the heel and throughout the middle of the bevel on the left hand side? Quite possible.

 

[OkayMode]

That was my thought too! I never saw a cladding that thin to be shown off only by removing low spots?

@Ok__mode_6953 I think you did a good job especially if you’re not doing it often. That’s the learning process!

But I would start with something coarser than a 1K stone, especially if you have low spots. It’s gonna be way faster and you will save a bit of your 1K stone too.

You could have saved your mirrored core by only applied your stone powder directly on the jigane if it was mirror finish or used some finger stones which can makes a nice finish.

Don’t give up! Polishing is fun but there’s a learning curve of course

Yeah I thought it was strange too!

I was using a reasonable amount of pressure, but did most of the work on the 1k, and wasn’t at it for very long compared to the hours long marathons I’ve heard on here!

Good advice here, thank you!

 

[Benuser]

No polisher here: first thing to watch is having enough core freed from cladding. On the right face at 3/4 from the heel and on the left one in the middle the line has become dangerously close to the very edge.

 

[OkayMode]

No polisher here: first thing to watch is having enough core freed from cladding. On the right face at 3/4 from the heel and on the left one in the middle the line has become dangerously close to the very edge.

Yep, those were definitely areas I wanted to try to push back, however I decided to stop when the blade was getting very thin - even though the cladding line hasn’t moved, the edge flexes under a nail when previously it didn’t. I think there must be something going on with the the grind in those spots.

 

[Blank Blades.]

I am a competent sharpener, but have very little experience thinning and polishing - something I am trying to change.

After failing to sell it, I decided to use my Manaka Shiro #2 Bunka as a practice knife. The cladding was reaching up to the edge in a few spots and has fairly flat bevels thanks to Manaka’s process, so this seemed like a good opportunity to make it more enjoyable to use and practice my technique.

I did most of the thinning with a Naniwa 1k, applying pressure evenly across the bevel at first from the edge up to the shinogi, identifying the low spots in the process.

I was able to mostly grind the low spots out by applying pressure at the edge and then moving the pressure upwards to reduce and eventually remove it, although I didn’t try to pursue it excessively with one or two particularly stubborn bits.

Similarly, I was able to push the cladding line back along most of the knife edge, but there are two spots which after a decent amount of effort refused to budge much. I decided to stop when the edge became nail flexing thin.

If you look at how uneven the hira is between both sides, I think the grind might just be a bit wonky, which makes sense as I bought this knife a little while ago when Manaka was less experienced and sought after than he is now.

After getting to a nail flexing edge along the majority of the blade save the heel, I decided I was broadly happy with the thinning job and stopped for the day.

Today I figured I would have my first ever go polishing, starting with a Morihei 500 and removing most of the really ugly stray scratches before moving on to an Imanishi 1k, getting the scratch pattern consistent, and finishing on a Morihei 3k.

I thought building up a slurry was meant to help develop an even finish, but I found if I let it build up, I would check my work and find a HUGE lone scratch requiring an additional 5 mins of buffing out - what’s that about?!

I decided I was happy enough with the finish on the stones when the core steel had developed a clean polish and the kireha had a nice enough kasumi with a consistent scratch pattern. There were definitely lots of deeper scratches I hadn’t worked out, but I know perfection requires a lot of time, effort and skill, so no dramas.

At this point I though ‘eff it, let’s get the Flitz and stone powder out to see if it helps cover up the low spots until I eventually work them out properly.’

I applied Flitz first with a cotton pad which pulled back the contrast on the kasumi significantly, but gave it a more consistent texture. It ruined my nice mirror polish on the core steel though, so I probably wont be doing that again.

I then used the stone powder, which returned a bit of contrast to the kasumi (although not as much as it had off the stones), and returned a bit of the polish to the core steel but nowhere near where it was before. The end result was less contrasty than off the stones, but better blended overall in my opinion.

I am happy enough with the result for someone very new to this, but am confident there are loads of things to improve - I just don’t know exactly what, and how to fix it!

Any and all feedback on what I need to improve and develop on is welcome, please point out any mess ups too!

Pictures show the before, video shows after.



Thanks for reading

What you did wrong. You decided to start stone polishing.

Your wallet and your soul will never be the same.

 

[OkayMode]

What you did wrong. You decided to start stone polishing.

Your wallet and your soul will never be the same.

Possibly the most helpful advice I will receive, but practical tips also welcome

 

[KenjiF]

I think there a 3 ‘types’ of high/low spots and each require a different approach to fix.

1st forged. Hammer hits the metal and makes a low spot where it hits and a high on opposite side…you will see i high spot on one side and a corisponding low spot on the other. These will usually be at shinogi line. You can grind these flat or take a hammer (brass hammer) and stump and even the spots out a bit if you want to make it more even. You will cause the blade to bend if you hit it with a hammer so will need to straighten.

2nd is the blade is bent or the warped. The warp or bend will mean parts of you knife are not touching the stone (looking like a low spot). You will usually see it on the other side but can be a little harder to see if it’s twisted instead of just bent. Solution- fix that **** before you hit the stones. A twist is usually hammer and stump or straightening stick and vice time. I’d reccomend taking it to a pro if it’s your first time on an expensive knife. You can snap blades trying to fix this. A bend is a simple fix and use a stick or a tabletop and the flat of your hand.

3rd is under/overgrind. Here you have to make the call if you want to thin the blade enough to fix. If the low spots are close to the edge and you don’t fix just make sure to keep checking the profile of the edge after sharpening to make sure there are no high spots or ‘holes in the edge’ (where part of the edge doesn’t touch the board when you’re cutting).

That does look like core steel to me popping through. It does happen when thinning sometimes. It will happen if the blade is bent when you thin and you keep grinding. Was the blade straight when you thinned?

 

[Blank Blades.]

I think there a 3 ‘types’ of high/low spots and each require a different approach to fix.

1st forged. Hammer hits the metal and makes a low spot where it hits and a high on opposite side…you will see i high spot on one side and a corisponding low spot on the other. These will usually be at shinogi line. You can grind these flat or take a hammer (brass hammer) and stump and even the spots out a bit if you want to make it more even. You will cause the blade to bend if you hit it with a hammer so will need to straighten.

2nd is the blade is bent or the warped. The warp or bend will mean parts of you knife are not touching the stone (looking like a low spot). You will usually see it on the other side but can be a little harder to see if it’s twisted instead of just bent. Solution- fix that **** before you hit the stones. A twist is usually hammer and stump or straightening stick and vice time. I’d reccomend taking it to a pro if it’s your first time on an expensive knife. You can snap blades trying to fix this. A bend is a simple fix and use a stick or a tabletop and the flat of your hand.

3rd is under/overgrind. Here you have to make the call if you want to thin the blade enough to fix. If the low spots are close to the edge and you don’t fix just make sure to keep checking the profile of the edge after sharpening to make sure there are no high spots or ‘holes in the edge’ (where part of the edge doesn’t touch the board when you’re cutting).

That does look like core steel to me popping through. It does happen when thinning sometimes. It will happen if the blade is bent when you thin and you keep grinding. Was the blade straight when you thinned?

All good advice.

I will say. Could be like you mentioned about forging. When they forge welded they surfaces could have been uneven. Leaving those odd thinner parts of cladding. Or something wierd going on after the initial forging before heat treating.

On top of everything you said.

 

[OkayMode]

I think there a 3 ‘types’ of high/low spots and each require a different approach to fix.

1st forged. Hammer hits the metal and makes a low spot where it hits and a high on opposite side…you will see i high spot on one side and a corisponding low spot on the other. These will usually be at shinogi line. You can grind these flat or take a hammer (brass hammer) and stump and even the spots out a bit if you want to make it more even. You will cause the blade to bend if you hit it with a hammer so will need to straighten.

2nd is the blade is bent or the warped. The warp or bend will mean parts of you knife are not touching the stone (looking like a low spot). You will usually see it on the other side but can be a little harder to see if it’s twisted instead of just bent. Solution- fix that **** before you hit the stones. A twist is usually hammer and stump or straightening stick and vice time. I’d reccomend taking it to a pro if it’s your first time on an expensive knife. You can snap blades trying to fix this. A bend is a simple fix and use a stick or a tabletop and the flat of your hand.

3rd is under/overgrind. Here you have to make the call if you want to thin the blade enough to fix. If the low spots are close to the edge and you don’t fix just make sure to keep checking the profile of the edge after sharpening to make sure there are no high spots or ‘holes in the edge’ (where part of the edge doesn’t touch the board when you’re cutting).

That does look like core steel to me popping through. It does happen when thinning sometimes. It will happen if the blade is bent when you thin and you keep grinding. Was the blade straight when you thinned?

I think @KenjiF might have nailed the reason for why there’s so much exposed core steel coming through at the shinogi on the right hand side of the blade towards the heel - there’s a low spot on the corresponding side which suggests it’s from hammering during forging.

Otherwise, the blade doesn’t seem bent or warped to me and the edge profile is fine.

 

[boblob]

No polisher here: first thing to watch is having enough core freed from cladding. On the right face at 3/4 from the heel and on the left one in the middle the line has become dangerously close to the very edge.

what does he mean by that ?

 

[boblob]

I think @KenjiF might have nailed the reason for why there’s so much exposed core steel coming through at the shinogi on the right hand side of the blade towards the heel

how do you know what is the cladding and what is the core steel ?

 

[OkayMode]

what does he mean by that ?

He means the cladding line (the soft iron that makes the san mai ‘sandwich’ with the core cutting steel in the middle) is very close to the cutting edge.

how do you know what is the cladding and what is the core steel ?

Do you see the wavy line by the edge of the knife? The metal at the cutting edge below the wavy line is the core steel and the metal above is the iron cladding.

 

[OkayMode]

A question - is it possible that the very bright spots by the shinogi, which we originally thought was the core steel coming through could actually be where I applied too much pressure and burnished the cladding?

I was using quite a lot of pressure with the 400 and 1k grits to try and push the cladding line up - possibly more than is sensible. I now know I should have done most of this work with a lower grit in the first place.

 

[Blank Blades.]

A question - is it possible that the very bright spots by the shinogi, which we originally thought was the core steel coming through could actually be where I applied too much pressure and burnished the cladding?

I was using quite a lot of pressure with the 400 and 1k grits to try and push the cladding line up - possibly more than is sensible. I now know I should have done most of this work with a lower grit in the first place.

No that definitely looks like core steel to my eye at least.

The spots on the left side of the knife at least. If that is what you are talking about.

After thinking about it again. Especially since its got that hammer tone. I definitely think the cladding got squished down there when forging that in before grinding. Exposing those wierd lines when you thinned it.

It being slightly hammered in one direction like described above also could have made it worse also.

 

[OkayMode]

No that definitely looks like core steel to my eye at least.

The spots on the left side of the knife at least. If that is what you are talking about.

After thinking about it again. Especially since its got that hammer tone. I definitely think the cladding got squished down there when forging that in before grinding. Exposing those wierd lines when you thinned it.

It being slightly hammered in one direction like described above also could have made it worse also.

I was referring specifically to the section towards the heel on the right hand side - just behind the lowest visible hammer mark on that side.

Appreciate your input though, it makes sense.

Kind of annoying that the knife I sacrificed to practice thinning and polishing has these inconsistencies I can’t really remove, but such is life!

 

[boblob]

Do you see the wavy line by the edge of the knife? The metal at the cutting edge below the wavy line is the core steel and the metal above is the iron cladding.

why did he remove all the cladding and expose the core steel?

 

[OkayMode]

why did he remove all the cladding and expose the core steel?

Read the thread again, the answer is already there - unless you mean why expose the core steel at the edge, for which the answer is because the core steel is the part that cuts

 

[boblob]

Read the thread again, the answer is already there - unless you mean why expose the core steel at the edge, for which the answer is because the core steel is the part that cuts

can you point me to to answer ?
why to remove a cladding completly and expose the core steel ? the cladding protects the core steel

 

[OkayMode]

can you point me to to answer ?
why to remove a cladding completly and expose the core steel ? the cladding protects the core steel

Here - read my comment, then Kenji’s.

I think @KenjiF might have nailed the reason for why there’s so much exposed core steel coming through at the shinogi on the right hand side of the blade towards the heel - there’s a low spot on the corresponding side which suggests it’s from hammering during forging.

Otherwise, the blade doesn’t seem bent or warped to me and the edge profile is fine.

If you’re still unsure, I would recommend either starting a new thread or spending some more time learning the fundamentals, as I don’t think you will pick up anything useful in this thread without that base knowledge and I would prefer to stay on topic.

 

[stringer]

can you point me to to answer ?
why to remove a cladding completly and expose the core steel ? the cladding protects the core steel

Imagine a pencil. If the wood cladding goes all the way down to the tip of the lead then the pencil won't write well. You need to expose the lead by removing the wood near the tip so that the writing edge can make contact with the paper. If the part of the knife that is capable of being sharp is covered up by stuff that is incapable of becoming sharp then the knife won't cut. The cladding protects the core steel in general but if it prevents the core steel from contacting the item you desire to cut then your knife has no real use for cutting things.

 

[Blank Blades.]

why did he remove all the cladding and expose the core steel?

Because he is evil, and wanted the core to be exposed.

 

[Blank Blades.]

I was referring specifically to the section towards the heel on the right hand side - just behind the lowest visible hammer mark on that side.

Appreciate your input though, it makes sense.

Kind of annoying that the knife I sacrificed to practice thinning and polishing has these inconsistencies I can’t really remove, but such is life!

I dont think i see any there

 

[dabes]

A question - is it possible that the very bright spots by the shinogi, which we originally thought was the core steel coming through could actually be where I applied too much pressure and burnished the cladding?

I was using quite a lot of pressure with the 400 and 1k grits to try and push the cladding line up - possibly more than is sensible. I now know I should have done most of this work with a lower grit in the first place.

It's really odd to me that the shiny spots on the right are all high up the blade, especially the spots near the tip, so you may have some merit in your thought.
Were those spots showing a different scratch pattern than the core off the low/mid grits too?

If you've collected any mud from flattening your stones, I'd rub some on those spots and find out

 

[OkayMode]

I dont think i see any there

 

[OkayMode]

Were those spots showing a different scratch pattern than the core off the low/mid grits too?

I can’t remember, but I was going to have another go polishing from around 500 grit or so to practice without taking away much more material, so I guess it should become apparent then.

Will post my progress!

 

[Blank Blades.]

View attachment 247991

Hard to tell. That might be burnishing? Only way to know is polish some more.

 

[OkayMode]

Hard to tell. That might be burnishing? Only way to know is polish some more.

Would you mind posting a similar screenshot highlighting the bits you think are exposed core steel, just for the avoidance of doubt? Cheers!