What to do with a stone that suddenly becomes scratchy?

[KenjiF]

One of my favorite suitas suddenly became very scratchy last week…

It has a little Suji but the scratchiness is coming from all over the face. I lapped a mm off it and tried again and it was ok for a bit but then again became scratchy. For other stones I’ve dug lines or avoided parts of the stone that are toxic but not sure what to do in this case. It’s not contamination. Do I just keep lapping and hope my beautiful suita comes back? The bottom is epoxy leveled so haven’t lapped through the bottom to check that side.

 

[musicman980]

Whenever this happens to me there are a few things I check to make sure it’s not some other variable. The most common problem by far is stone edges that are not rounded enough, so they chip out very easily especially under a diamond plate. I’ve also done corners with sandpaper just for good measure. Then check the diamond plate itself for any damage to it like a dinged corner or a protruding diamond.

Are there any micro cracks/checks in the stone’s surface? Your suita looks relatively clean.

 

[lesslemming]

Hey Kenji, sorry to hear that your Maruoyama got scratchy. That’s a real bummer, but I wouldn’t be panicking just yet.

If the stone wasn’t scratchy a few days ago, something must have happened. Becoming scratchy at every point is unusual and does not necessarily point to an inclusion. So I’m still hopeful there must be another reason.

Did you lap off a generous amount before this happened?

Can you show us the scratch pattern? Is it consistent or are the scratches random?

Do you have another, similar stone to check if it might be the blade that’s causing the issue?

I had a Nagura that would throw random scratches and stopped after soaking it for 2 days (beware of cracking).

Did you try lapping the stone a little coarser or a little finer than before to see if the situation changes? Too rough can cause lumps of particles breaking loose, too fine may cause pulling iron (although both should not be a problem with a Maruoyama)

 

[KenjiF]

Whenever this happens to me there are a few things I check to make sure it’s not some other variable. The most common problem by far is stone edges that are not rounded enough, so they chip out very easily especially under a diamond plate. I’ve also done corners with sandpaper just for good measure. Then check the diamond plate itself for any damage to it like a dinged corner or a protruding diamond.

Are there any micro cracks/checks in the stone’s surface? Your suita looks relatively clean.

Thanks I’ll give that a try. I’m flattening with nanohone and I haven’t found it to shed any diamonds. I didn’t check the edges though that’s a good call.

 

[KenjiF]

Hey Kenji, sorry to hear that your Maruoyama got scratchy. That’s a real bummer, but I wouldn’t be panicking just yet.

If the stone wasn’t scratchy a few days ago, something must have happened. Becoming scratchy at every point is unusual and does not necessarily point to an inclusion. So I’m still hopeful there must be another reason.

Did you lap off a generous amount before this happened?

Can you show us the scratch pattern? Is it consistent or are the scratches random?

Do you have another, similar stone to check if it might be the blade that’s causing the issue?

I had a Nagura that would throw random scratches and stopped after soaking it for 2 days (beware of cracking).

Did you try lapping the stone a little coarser or a little finer than before to see if the situation changes? Too rough can cause lumps of particles breaking loose, too fine may cause pulling iron (although both should not be a problem with a Maruoyama)

That one is my shobu suita. The Mauroyama has some Suji in it and I’ll dig it if it starts scratching but this stone has not performed badly until this week. I’ve tried it on a few knives.

It is a harder stone and can pull iron if I don’t dress it well or use too much pressure. But never like this. I’ll get some images of the finish it’s leaving.

How could the knife be the problem? The iron too soft, KU releasing and causing scratches?

I lapped about 1mm off with the nanohone, cleaned the stone really well and started polishing again and it was fine for about 5 minutes and then it would get scratchy again. Also very little crunching feedback and I didn’t notice until I checked my blade…

Thanks for the suggestions.

 

[SwampDonkey]

Out of curiosity, what does "pull iron" mean in these cases?

 

[KenjiF]

@SwampDonkey On harder stones if you apply too much pressure, dress the surface too coarse, use not enough water, too much or look at it wrong it catches the soft iron and puts a big scratch on the iron.

The reason I don’t think this is ‘pulling iron’ is because the feedback isn’t changing. It’s pretty obvious to me when the blade catches but this is different feedback. It’s like the grit of the whole stone has gotten coarser…

As a side note this stone has drastically changed appearance since I’ve bought it and used it. I’ve had layers with kuro renge, aka renge and an almost sumengashi patterning on the stone. Right now it’s pretty uniformly white except for the Suji…

 

[lesslemming]

Ohhh, I see. I thought that was your new Maruoyama.

Alright then, forget what I said (partly).

I remember you told me the stone changed appearance significantly and that of course means you could be uncovering some toxic areas. That is super unfortunate. I did not have that happen to me but I’d imagine I would try to lap past the bad part of it if feasible

 

[KenjiF]

Ohhh, I see. I thought that was your new Maruoyama.

Alright then, forget what I said (partly).

I remember you told me the stone changed appearance significantly and that of course means you could be uncovering some toxic areas. That is super unfortunate. I did not have that happen to me but I’d imagine I would try to lap past the bad part of it if feasible

Lapped another mm off and rounded the edges and the stone started working well again. Not sure what it was but seems to be ok for now. Thanks for all the advice!

 

[M1k3]

Have you tried soaking it in warm water? I think it was @EricEricEric who suggested this for softening stones up. I have no idea if that would actually help with your issue though.

 

[KenjiF]

Have you tried soaking it in warm water? I think it was @EricEricEric who suggested this for softening stones up. I have no idea if that would actually help with your issue though.

I've done that with super hard stones to make them softer and scratch less. I'll give it a try if the scratchiness comes back. It was the first Jnat I bought and I've probably spent 100+ hours on that stone so it's more about why it was behaving differently to what I was used to...

 

[KasumiJLA]

I had the same problem on my Maruoyama Aisa one day. I always had the same type of finish and overnight I had random scratches. I know you ruled out cross contamination but for me it was exactly that problem. Surely diamonds have impregnated on the surface (invisible to the naked eye) and this is what caused the problem.

I changed the diamond plate and removed a good 1mm. I rinsed like there was no tomorrow and scrubbed with a medium synthetic wool. Everything went back to normal!

Good luck and I hope you will fix that problem!

 

[KenjiF]

I had the same problem on my Maruoyama Aisa one day. I always had the same type of finish and overnight I had random scratches. I know you ruled out cross contamination but for me it was exactly that problem. Surely diamonds have impregnated on the surface (invisible to the naked eye) and this is what caused the problem.

I changed the diamond plate and removed a good 1mm. I rinsed like there was no tomorrow and scrubbed with a medium synthetic wool. Everything went back to normal!

Good luck and I hope you will fix that problem!

The reason I ruled out contamination is that I recently switched to nanohone nl8 for flattening and to my knowledge it doesn’t shed diamonds… I also washed the stone and scrubbed it and still saw problems.

That being said I did ‘refresh’ the nanohone on some sic powder and that might have transferred somehow now I’m thinking about it…

Thanks mate.