Gray sludge that looks like neither slurry or swarf

[Miguelito's Blade]

So I picked up three damaged knives on ebay to practice on. When I took one of them to a coarse stone to start refinishing it, I noticed that a gray sludge formed immediately after a couple of strokes. I wiped it off, and it just smeared onto the blade and instantly dried. It would not wipe off, but instead stuck to the metal and dulled the area that I had just abraded. It would not wipe or wash off completely. Both of the other knives did the same thing. It simply makes too big a mess to continue, leaving me on the verge of tossing them. First, however, I would like to find out what it is.

 

[Benuser]

What stone and steel is it about?

 

[Miguelito's Blade]

A 220 Shapton ceramic and a 500 Shapton glass. The steel, as far as I can tell, is stainless, based only on my extremely limited experience and knowledge of steel. In other words, I could not find anything that indicated to me carbon steel such as evidence of clad construction. I purchased a lot of three knives, and all three produced the same substance. I have attached a photo of the deba (the other two are a yanagiba and an usuba).

 

[ModRQC]

Looks like a mono carbon to me.

I'm also failing to see the area you're talking about.

 

[Benuser]

From the stain I would say it's indeed a monosteel carbon. I wouldn't be surprised if it was a accumulation of debris on top of the former edge. You stopped to early, I guess.

 

[ModRQC]

From the stain I would say it's indeed a monosteel carbon. I wouldn't be surprised if it was a accumulation of debris on top of the former edge. You stopped to early, I guess.

From what he said I think he was polishing - more surface was involved. But basically the same answer applies.

I'm guessing it will resolve as clear steel will have been exposed.

 

[Miguelito's Blade]

Thanks for the replies. I'll keep grinding. Also thanks for cluing me in as to the type of steel.

 

[M1k3]

Did you wash them before sharpening? Could be old oil residue.

 

[Miguelito's Blade]

I did wash them. I scrubbed the bejesus out of them and turned some of the kanji characters from black to white. I've been working on the usuba and will post some photos later tonight of how the gunk turns a bright ground blade into a dull mess.

 

[M1k3]

Clean them up with a paste made of baking soda and lemon juice (or other citrus) first. Sounds like the patina is really heavy.

 

[mengwong]

If that doesn’t work, the next option would be BKF, but neutralize with a round of baking soda after. I was going to say “nuclear option” but that would be dehandling and applying lye in a bag? Only to be considered if you are already making pretzels.

 

[mengwong]

Could it be “flash rust”, but “flash patina”? I wonder if sandpaper with oil would go differently.

 

[Miguelito's Blade]

In the first photo, I have been grinding it with 60 grit sandpaper and it is bright and shiny. In the next photo, I have made six passes on a 220 grit Shapton ceramic stone, which produced the gray substance leaving the blade gray and dull. The only way to remove it that I have found so far is to return to sandpaper.

 

[mengwong]

Fascinating. If you do sandpaper and then 500 does it recur? I assume your 220 and 500 have been flattened / lapped appropriately, possibly against each other.

 

[Miguelito's Blade]

Both stones have just been flattened with a diamond plate and cleaned with a nagura stone. What makes it all the more puzzling to me is that all three knives do the same thing.

 

[jjlotti]

Did you wash them before sharpening? Could be old oil residue.

This. With spring coming I just tuned up my bypass pruners... It had been several years since I had taken then all the way apart so long story... Started lapping the blades with a india and got pretty much what your describing. With their nature of cutting vines and stems then not ever really getting washed the oil and plant material just builds up. Think range hood type buildup on your knife? Never underestimate the other guys Nast....
For the old earned patina lovers

 

[mengwong]

May I suggest an experiment, since you have three …

A: sandpaper to shiny, then dry and leave in air
B: sandpaper to shiny, then dunk tip down, half in water for 20min. Are you using fresh tap water or the stuff in the tub?
C: sandpaper to shiny, then SG500 polish tip half, one side only

Let's see what causes the gray …

 

[Miguelito's Blade]

Great suggestions. I will try them today and post the results.

 

[stringer]

In the first photo, I have been grinding it with 60 grit sandpaper and it is bright and shiny. In the next photo, I have made six passes on a 220 grit Shapton ceramic stone, which produced the gray substance leaving the blade gray and dull. The only way to remove it that I have found so far is to return to sandpaper.

It looks to me like the grey dull area could just be the scratch pattern of a 220 grit stone. It also looks to me like you might be dealing with a clad knife that was sharpened in such a way that the cladding goes right down to the edge. And when you are sharpening you are revealing the core steel which is a different color. I would probably not worry too much about what it looks like until you get it tuned up, thinned a little to see if you can detect a clad line, and sharpened. Not much point in worrying about aesthetics on a fixer upper until you get all that straightened out. Then you can makee a decision about whether you want a stone finish or a sandpaper finish, or whatever.

 

[DanielC]

If you are grinding bare metal and still experiencing this mud building, fancy the crazy idea that these might be some sort of Korean or Chinese knives made from cast iron.

The characteristics sound like cast iron to me in the machining world. I never thought someone would try to make a knife out of this, but I googled and found there were cheap lines of knives out of Korea that advertised being cast iron. One guy even made a video showing how quickly it dulls.

 

[ModRQC]

I might be wrong but the inscriptions on the blades look like Japanese to me.

If the steel is indeed heavily patined, the regular mud with many stones turns out sticky and clinging like crazy unless using lots and lots of water on the stone.

If the blades once polished with sandpaper to bright still do that, @stringer theory of clad could make sense. Also, while I never worked with it particularly, I'm guessing White #3 would generate some kind of real ugly swarf, if I think of my experience with White #2 rather ugly one. Especially I've worked with brand new knives mostly, but if these have seen dishwasher and lots of such abuse, I guess it could very well be "naturally nasty" for a good layer of steel before possibly getting to good steel. Then @stringer proposition seems the only way to go: thin, get an edge, see how it goes. If you can't get an edge to hold for all your efforts, you might be facing such an issue as I'm pointing out. Or also that Stringer is right and you're basically sharpening cladding until you'll have thinned it enough to get some core steel out of there.

 

[Miguelito's Blade]

As far as I know, they are all Japanese. When I purchased these three knives, I also purchased another usuba from a different seller. Upon taking it to my 220 stone, it did the same as the others, as the previously shiny areas became covered with the same substance. The fourth photo is my 220 Shapton ceramic stone. The dark area appeared after first working on the first knife. I thought it must be just drying unevenly when the dark spot remained after using it. However, overnight it did not diminish at all, so I can only assume that it was stained by the same stuff.

I realized that buying damaged Japanese knives on ebay was a gamble, but not in this manner.

 

[mengwong]

So the current hypothesis is that the stain is spreading from the stone to steel?

If you flip the stone and run it against a knife from your pristine collection does it happen? And then does it happen when you run your known good knife against the stain?

 

[ModRQC]

Am I seeing a clad line on the closer picture of the cutting side? Could be nimai. Iron cladding of old might explain the behavior on the stone.

 

[Miguelito's Blade]

Am I seeing a clad line on the closer picture of the cutting side? Could be nimai. Iron cladding of old might explain the behavior on the stone.

Yes it is a clad line. As I understand it, nimai cladding is a carbon core clad in iron. Is iron known to produce such a substance? If it is, then all four knives are trash.

 

[Miguelito's Blade]

So the current hypothesis is that the stain is spreading from the stone to steel?

If you flip the stone and run it against a knife from your pristine collection does it happen? And then does it happen when you run your known good knife against the stain?

No. That is not happening because I've tried both ways you suggest and a good knife against either the stained side or the clear side produces nothing other than what it always produces. When I first realized that the stone was stained with this substance, I feared that my stone was damaged but it wasn't.

 

[stringer]

Yes it is a clad line. As I understand it, nimai cladding is a carbon core clad in iron. Is iron known to produce such a substance? If it is, then all four knives are trash.

It looks to me like you just need to go further. Soft iron will sometimes get gummy/smeary like you are describing. Soft stainless can too. Old Chinese carbon cleavers. Axes and hatchets. It's not a big deal. The discoloration will not affect how the knife or stone work in any way whatsoever in my experience. If you want to get rid of the staining from either I suggest a green Scotchbrite pad or similar and a bit of scrubbing. The knives are trashed but probably not trash. As in, they have not been cared for very well but they can probably be salvaged if you are willing to put in the time and energy. No shame if you don't have the time or energy either. I have drawers full of half finished project knives in similar condition. But the only way the knives are truly trash is if they won't hold an edge and you have not done enough work to determine if that is true yet or not.

 

[Miguelito's Blade]

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It looks to me like you just need to go further. Soft iron will sometimes get gummy/smeary like you are describing. Soft stainless can too. Old Chinese carbon cleavers. Axes and hatchets. It's not a big deal. The discoloration will not affect how the knife or stone work in any way whatsoever in my experience. If you want to get rid of the staining from either I suggest a green Scotchbrite pad or similar and a bit of scrubbing. The knives are trashed but probably not trash. As in, they have not been cared for very well but they can probably be salvaged if you are willing to put in the time and energy. No shame if you don't have the time or energy either. I have drawers full of half finished project knives in similar condition. But the only way the knives are truly trashed is if they won't hold an edge and you have not done enough work to determine if that is true yet or not.

I have intended to find out if any of them will sharpen. If not, then that ends the project right there; however, if they will take an edge, then I will spend the time and effort to refinish them. As luck would have it, I am disabled and have all the time in the world to work on knives. And I don't mind the effort I will have to put into it, which I knew I would put into all of them when I started looking for old beat up knives on ebay.

The general consensus seems to be that I need to keep working on them to try and remove enough of the outermost metal to reach "good" steel beneath. At this point I'm not at all confident that good steel is there to be found, but it doesn't hurt to look.

 

[ModRQC]

-

I have intended to find out if any of them will sharpen. If not, then that ends the project right there; however, if they will take an edge, then I will spend the time and effort to refinish them. As luck would have it, I am disabled and have all the time in the world to work on knives. And I don't mind the effort I will have to put into it, which I knew I would put into all of them when I started looking for old beat up knives on ebay.

The general consensus seems to be that I need to keep working on them to try and remove enough of the outermost metal to reach "good" steel beneath. At this point I'm not at all confident that good steel is there to be found, but it doesn't hurt to look.

Well it’s also iron clad to begin with. When I put any carbon/iron onto stone like Cerax 1K, it will discolor it especially in polishing and if I don’t see to it, eventually there’s not much cutting action happening and the mud turns bad. I have plenty stones to elect not to use that one in any case scenario, but if I do, then it needs the Atoma often is all. And these are brand new knives I’m talking about.

Now that we know what we’re dealing with, you could be experiencing something similar. I don’t have the SP220 so can’t discuss of its behavior.

 

[Miguelito's Blade]

Well it’s also iron clad to begin with. When I put any carbon/iron onto stone like Cerax 1K, it will discolor it especially in polishing and if I don’t see to it, eventually there’s not much cutting action happening and the mud turns bad. I have plenty stones to elect not to use that one in any case scenario, but if I do, then it needs the Atoma often is all. And these are brand new knives I’m talking about.

Now that we know what we’re dealing with, you could be experiencing something similar. I don’t have the SP220 so can’t discuss of its behavior.

I experience the same thing with my good knives, i.e., they discolor the stone; however, the discoloration is nothing like what I am experiencing. I don't think that you are referring to the ordinary swarf that forms, because even though it discolors, what doesn't wipe off is easily removed with a diamond plate, or, for that matter, with a nagura stone.

As to the nasty stuff that won't wipe off at all, it is going to require a diamond plate, and I don't know yet if the stain is just on the very surface or if it extends down into the stone. I've never seen anything like this with any of my good knives on any of my stones. I'll know more as soon as I get to my workbench today.