Jnat slurry colour change

[RobbyC]

Just wondering if any of you gents have had the same experience or could possibly give a bit of insight.
Two of my jnats have a similar reaction though this one much more so.

The stone in question is an Aiiwatani San from Maksim, a very very fast stone with slurry, darkening straight away.

If I stop honing and leave the slurry for even a short time it quickly turns light brown as (I assume) iron oxide forms.

Only 2 of my jnats do this, and I have had one coticule in the past which has a similar reaction.
Is this simply a case that the steel being removed is of such fine particle size that it oxidises rapidly due to high surface area, or could it be something potentially corrosive within the stone which is forcing oxidation.

I have not noticed any rusting of the edges honed on the stone, though I probably don’t leave slurry / water on them long enough anyway.

Anyone had a similar experience ?

Thanks in advance

Rob

 

[alex1921]

I have seen it with suitas, I was told that some of them have lower pH and they oxidize the iron in the swarf.
From all the stones I have tried the only one that actually damaged the test razor was a black renge suita. It would leave these black dots/marks on the bevel under the microscope.

 

[eKretz]

Yes absolutely.. It is likely a combination of factors that causes this. The very fine particles abraded from the steel is one of those. Then the makeup of the stone itself when you create a slurry is another. The mineral content, pH and perhaps salt content (water softener, anyone?) of your water is another.

Try an experiment and hone on a very fine diamond plate with the same razor. Does the swarf begin to rust? If so, probably your water. If not, your stone plays in. If it is the stone you can prevent most problems by rapidly drying your razor after honing. You can also add a bit of baking soda to the water you use on the stone, this will help as well.

 

[Herrenberg]

Fascinating thread.

 

[stone and strop]

I use only distilled water on all my hones - even synthetic.
It just takes simple variables out of the equation.

 

[Steve56]

Yes, it is interesting.

I’ve been talking with Alex Gilmore in the past few days about ‘staining’ stones, ones whose slurry would change the color of steel. He told me that soft uchigumori was the prime suspect, but obviously several other examples in several layers exist, including some colors of renge in ‘floor’ suita.

Maybe @alx gilmore could shed some light.

Cheers,

Steve

 

[Gamma]

Many stones darken when they get wet. And get even darker as they saturate further. Sometimes, slurry will darken similarly.
If you make slurry with a non-ferrous something, and the slurry still darkens, you will know it's not getting darker due to steel particles oxidizing in it or some sort of chemical reaction with steel.

If you are working the blade enough, you can shed enough steel to darken the slurry and if that stone's slurry keeps the particles in suspension well enough (viscosity) then the slurry will darken.

The stone particles in the slurry can oxidize as it aerates with agitation. Like some stones just get darker with age, but we're speeding up the process a bit.

Stones with a ph that will cause the steel to oxidize are not that common, they do exist but it's not like there's another one around every corner.
A simple PH kit will put the thought to rest. Some users will add baking soda to water but it's really not something that needs to be done unless there is an actual proven issue.
Someone used to recommend using distilled water until another someone pointed out that distilled water will remove minerals from the stone and that prob wasn't a good idea. That wisdom disappeared from the guys website pretty quickly. Prob didn't matter either way but that's how misinformation gets spun around in the inter-tubes.

Some Suita, like Enshou, can cause grief, some others too. Usually not stones from Tomae, Aisa, or Namito though.. but it's not totally out of the realm of possibilities. We never know what soaked into what stones over time. Anything is possible.

But, fwiw, slurry getting darker is pretty common. Without seeing your slurry in action here in my house I don't know for sure what the story is though. Just sayin' - slurry getting darker happens a lot here. If you don't have any visible issues on your steel, that's a good sign that all is well.

 

[C FrankC]

I have one stone in particular that is more acidic, will stain certain steels more than some others. I have experimented enough to know it's this particular stone and not the water or nagura's.
This is not altogether uncommon so I've been told according to sources I trust.
When I hone using this stone, especially if I'm running full progressions = more time on the stone, I mix Calcium Bicarbonate into the water that use to hone with, this corrects the PH.
Natural stones never cease to amaze me.

Frank

 

[eKretz]

Another variable I forgot to mention also is the steel itself. Certain steel alloys are more prone to rusting than others. Obviously you shouldn't see this happen with a stainless razor.

In any case, I side with those who say it can be safely ignored if it isn't causing any issues with your razor.

 

[RobbyC]

Thanks for the replies all!
I will do some further testing tonight and see what I can figure out.

Water where I am is hard, with a lot of dissolved calcium.

And I have honed 100+ razors without my tap water causing any noticeable problems.

I’ve had the same effect with the same stone on multiple razors.


pH test of tap water vs slurry puts them very close, the slurry test being on top (light slurry left for a minute before testing)

Slurry was close to neutral pH, slightly more acidic than plain tap water

At work now but I will take slurry from a few stones and leave it sat on a beater blade to see if it stains it in any way.
And mix up some slurry and see if it changes colour on its own.

Regardless of what is causing it, the stone gives wicked edges so I will continue to use it.

Rob

 

[cotedupy]

I'd be semi-sure this is acidity causing oxidation. It happens in varying degrees on different stones (ime), and fun to play around with... if you leave certain jnat mud to dry on knives you can get a kinda etching effect on the cladding which is quite cool.

(Probably not recommended for razors though!)

 

[Matt O]

I use only distilled water on all my hones - even synthetic.
It just takes simple variables out of the equation.

I use distilled water when I bowl lather, and it makes sense to me! I will start doing this when honing as well.

Vr

Matt

 

[alx gilmore]

I have observed this same reaction of stone slurry, black swarf and steel staining.

Alx

 

[alx gilmore]

First & second photo same blade and stone leaving etched pattern, the third photos different stone that left a simple foggy kasumi pattern without the etched effect even if the slurry was left on the blade.

Alx

 

[RobbyC]

First & second photo same blade and stone leaving etched pattern, the third photos different stone that left a simple foggy kasumi pattern without the etched effect even if the slurry was left on the blade.

Alx

I have tested the stone again tonight,
I left the slurry to dry out for 24hr and rehydrated it and then honed the same razor again, the slurry didn’t change colour in the same way, it went brown(ish) after maybe 15 - 20 mins

I then refreshed the slurry and used a different razor (old battered silver steel thing) and again the colour change didn’t happen, though leaving the slurry on the same blade left a forced patina where it had been.

So I guess a combination of everything above!

I guess it is something released from clay binder, maybe CO2 forming carbonic acid in solution then disappearing.

Cheers for the replies gents

Rob