Pennsylvanian Whetstones

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musicman980

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PA Whetstones

For the past few years I have been searching my native Pennsylvania for a suitable whetstone material. We have rocky soil, boulders strewn about the landscape, and plenty of shale and slate outcroppings, and almost all of it is too hard and scratchy. Eventually I discovered a type of stone that performs extremely well as a polisher and sharpener once you know its intricacies. It’s an elusive and sensitive stone.

I’ve been wrestling with these stones for a while trying to figure out how they work. Sometimes they gave amazing finishes, other times they were too scratchy. These aren’t the types of stones that just hand you amazing finishes without due diligence. There are certain stipulations that make these stones a little more sensitive than your average stone, but the rewards are clear as day. As a polisher, the contrast is untouchable by any Japanese stone I have ever used. Cores that are deep mirrors, and claddings that are perfectly opaque. Streaks are completely eliminated with ease, and spot treatments blend in instantly.

These pieces have an unusual characteristic with regards to their hardness. Slurry pours out of them under a diamond plate, making them seem extremely soft. But under a knife blade, they hardly release anything at all. They act hard or soft depending on what you rub on them. Anything with a grit, like the micro protrusions of a diamond plate or sandpaper engages with the stone’s surface and releases a ton of slurry, but anything that is smooth like the bevel of a knife or razor doesn’t catch the surface in the same way and the stone’s particles stay locked in place.

There are a few extremely useful characteristics of these stones. The first is that they give the same level of polish with or without slurry. So, if you accidentally scratch your bevel on water only, you can raise a slurry and take out the scratches without taking any steps backwards. This works quicker on cladding scratches, as the stone is much gentler on the hard core. The second is that they completely eliminate any streaking. No matter where I focused my pressure, or where I did any spot treatments on the finish, the work blends in instantly with the surrounding area. It really is unbelievable.


Some stipulations to keep in mind: (1) They are sensitive to diamond plates. If your plate is too fresh or too aggressive they tend to release larger chunks of grit that can scratch your bevel. I use a PA nagura or the worn out part of my atoma 400 and the slurry is much cleaner. (2) They are really thirsty stones. (3) Most scratches visible on the hagane before you use the PA stone may still be there after, just more mirror and in heavy contrast with an opaque cladding. I used a Nakayama with slurry before going to the PA stone just to clean up lower grit scratches, and this helped a lot with the final finish.

I don’t know how these perform on honyaki, but I would love to find out.

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Are these stones that you bought cut and flattened sold as sharpening stones? I'm imagining you walking through the woods and picking up rocks to flatten and test out. :)

I'm starting to think your polishing abilities allow you to just pick up a rock, rub some steel on it, and get a fantastic kasumi, lol.
 

sansho

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how are you flattening random rocks for testing?
 

musicman980

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Once you get them dialed in with a nice fine slurry they are a dream to use. You hear and feel a lot of fine abrasion with slurry, which makes for great feedback. So far I’ve tested them on simpler steels, but I do have some aogami super next in line.
 

KingShapton

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Congratulations, that looks amazing!

What a great find. 👍

Normally I'm more into sharpening and hardly into polishing, but these results are stunning!!
 
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musicman980

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They bring out a lot of contrast on AS too. The core looks a little grainy up close, which I guess is the grain of the steel? When I first saw that effect I reset the finish on a fine Nakayama with and without slurry, then redid the PA finish and got similar results.

These seem to perform a lot like uchigumori but with exaggerated effects. Like uchigumori, I think what’s happening here is that the particles themselves are generally coarse but also soft so they resist scratching hard steel. They make the jigane super frosty and more or less buff the hagane.

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sansho

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i wonder what those are. are they slate?

got any friends who are geologists or something? it would be cool to ask a rock guy's opinion.
 
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I hiked the Pennsylvania portion of the AT once upon a time, and had the bone bruise to prove it. Nice seeing those rocks put to work grinding something other than my boots!

Along similar lines, Mortise and Tenon magazine did a video where they went to an old quarry site and found some stones that they flattened for honing. (Not sure if that's come up in other threads before).
 

musicman980

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i wonder what those are. are they slate?

got any friends who are geologists or something? it would be cool to ask a rock guy's opinion.
I'm pretty sure these are a type of slate, though they act very differently from all other slates I've tried. Most slates are harder and often a lot less fine, while these are softer and finer with softer grit particles.

I hiked the Pennsylvania portion of the AT once upon a time, and had the bone bruise to prove it. Nice seeing those rocks put to work grinding something other than my boots!

Along similar lines, Mortise and Tenon magazine did a video where they went to an old quarry site and found some stones that they flattened for honing. (Not sure if that's come up in other threads before).
I can tell you they weren't found at any quarry, but I think I have seen that video you mentioned - pretty inspiring. They do sharpen very finely, but they really excel at polishing. I wouldn't be surprised if they were never exploited for sharpening before because this level of polish is more of a modern consideration in this part of the world.
 

musicman980

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Heiji semi-stainless core with stainless clad. This seems to be a coarser example of the PA stones, or at least it’s acting that way with this Heiji. Check out the artifacts that appeared in the core - I'm pretty sure it's not corrosion, so perhaps it's the grain of the steel?

The original finish:
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The PA finish:
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musicman980

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That looks like a very fine and fairly hard stone. Great find! Any plans for razor testing?
It actually doesn’t feel very hard at all, and that’s the interesting thing about these stones. I think they are a softer type of stone. They are very forgiving under the blade, and it feels very appropriate using a lot of pressure. The particles themselves must be soft yet so fine.

I have honed a razor on one and got a really great shave, but that was only once. More testing is definitely needed. My hunch is that you could finish a razor with a lot of slurry, in fact a thick slurry might be required since I think the particles are quite soft.
 

musicman980

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Speaking of Pennsylvan-iangan, these do need a name. I’m not into names like “black shadow” or “stone of a thousand truths”, maybe something a little more direct.

I found this little guy yesterday and he seems like a winner. The key to unlock this one - work a thick slurry until it’s dry and the contrast will explode.

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Looks kinda similar to when i was using loose 1000 aluminum oxide grit to polish. The hard steel would mirror way higher than 1000 grit, and the soft iron would look hazy and very whitish. I also had to build a slurry of sorts, and work it until it was thicker and almost dry. I added a little detergent to help suspend particles better, and maybe the natural substances in the stone help that happen during sharpening
 

musicman980

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Looks kinda similar to when i was using loose 1000 aluminum oxide grit to polish. The hard steel would mirror way higher than 1000 grit, and the soft iron would look hazy and very whitish. I also had to build a slurry of sorts, and work it until it was thicker and almost dry. I added a little detergent to help suspend particles better, and maybe the natural substances in the stone help that happen during sharpening
Thank you for sharing that, it sounds similar to what’s going on here. These stones are thirsty which helps a lot with drying out the mud. Finishing that kanna blade took maybe a minute.
 

musicman980

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I’ll be the obnoxious greedy one saying what many of us are thinking - pass around so we can all experience the new gold standard? 😅

I would like to get some of these out into the community because there is so much potential here. I've already gotten a few requests, if anyone is interested send me a PM. 👍
 

cotedupy

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Top stuff C! Those are some amazing finishes :).

What is it that makes you think they're slates btw? Given your descriptions of them and the pics, they don't seem like slates to me. I'd be reasonably confident they're shales - because of the sedimentary appearance to the surface combined with fissility in the structure.


(Or an outside chance on some kind of slightly siliceous carbonate - you could test this with acid.)
 
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