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Pennsylvanian Whetstones

Couple raw stones that have not yet been cut into hone shaped objects...
 

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Pretty sure i also have a couple of that stone. Looks very similar anyway. Have you tried out Pennsylvania bluestone? I think it is mined in the northeast (NEPA to the locals) but is available all over the state. I picked up a large piece from the local landscaping supply. Sandstone, feel like it would be coarser then a queer creek. Slow and course with water but fast and fine with slurry. When the weather gets better i want to put a few pieces in my kiln and heat-treat? them. Read somewhere, grinding and honing i think, that heat will change the characteristics of the stone. I have plenty of it so why not.
I did try out the bluestone a few years ago, it was really hard and coarse to me. I have never heard of heat treating natural stone, let me know if that works.

Those slates/shales look like they might do the job, and I'm very curious about that x-large newly mined slate.
 
I did try out the bluestone a few years ago, it was really hard and coarse to me. I have never heard of heat treating natural stone, let me know if that works.

Those slates/shales look like they might do the job, and I'm very curious about that x-large newly mined slate.
Big piece of slate is only 1/4 thick. I am curious to try it also. Got it as a sample.
The third volume of "grinding and honing" has a little write up about heat treating naturals. I think they got softer if memory serves but the was all it really talked about. The interesting thing about the bluestone is that it is night and day different with or without slurry.
 
Here is a piece I just sealed in a batch of stones. It’s hard, and there were a few cracks in the sides that needed sealing with CA before the spar urethane. One of the cracks was sizable and part of it went up across the layers. I thought a slate would split along the layers, so perhaps this is a hard shale. 210 x 60 x 36

I worked up a slurry with a worn atoma 400 and worked that slurry for a while, very slowly diluting it and actually finishing on a thicker slurry than I normally would (compared to a jnat finishing slurry). The shave test will have to wait for a few days.

The point of all of this isn’t so much to find the best razor honing material in existence, or start a hole mining operation. There are a lot of legendary razor hones out there with established reputations. These past few years of rock hunting were a part of a switch in mindset - moving further away from mass production and into local goods and services. At the end of the day I feel better eating a meal with locally grown food, on a plate made by the local potter, at a table I made myself from local wood. Even finding a single rock that can do the job would be amazing, because then they become tools again. This isn’t a flashy Nakayama maruka kiita sports car that I bought just to show it off, this is a rock fine enough to finish a razor, and I found it at the creek.


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Just quick tests. First is of the bluestone with slurry. Bluestone scratches are diagonal. Definitely can see the contrast it creates. Second is of the gray shale.
Gray stone has a brownish purple slurry darker then the picture shows.
 

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I keep looking at this piece of quartz the size of a football at my mom's house but i know it would be a lot of work to break down and almost definitely disappointing as a hone.
 

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Found another. Red shale, this stuff is all over the place near me. Still have to lap this one so i can test it. Pretty sure it is loaded with iron oxide.
 

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Bluestone ready for the kiln

You put them in the kiln to harden them?
Some potters “calcine” hard natural stone, which is baking them at very high temperatures to make them more friable so they can break them into dust for glazes. Maybe @Pack line is doing something similar here? Friability is a good thing for jnat grit, but as for making the entire stone friable we’ll see if that’s a good thing.

*Edit* WARNING - Some rocks like shales, slates, mudstones, schists, limestones and others can explode when heated to high temperatures! I wouldn't recommend doing this.
 
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Some potters “calcine” hard natural stone, which is baking them at very high temperatures to make them more friable so they can break them into dust for glazes. Maybe @Pack line is doing something similar here? Friability is a good thing for jnat grit, but as for making the entire stone friable we’ll see if that’s a good thing.
I've got a forge and a piece of welsh slate I'd like to be more friable. That's a thought.
 
I've got a forge and a piece of welsh slate I'd like to be more friable. That's a thought.
Warning!!! Some rocks like shales, slates, mudstones, schists, limestones and others can explode when heated to high temperatures! I wouldn't recommend doing this.
 
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Just trying an experiment. Most clays change properties at 900F, something about the molecular water i think. The binding in the stone should be some type of clay. Going to be a slow heat to make sure any water that is trapped in the stone safely leaves. Hoping to soften the stone a little because it definitely works better with slurry but it will not auto slurry. The slurry already feels friable under a blade. There is a section in the 3rd volume of grinding and honing about heating stone.
 
Some potters “calcine” hard natural stone, which is baking them at very high temperatures to make them more friable so they can break them into dust for glazes. Maybe @Pack line is doing something similar here? Friability is a good thing for jnat grit, but as for making the entire stone friable we’ll see if that’s a good thing.

*Edit* WARNING - Some rocks like shales, slates, mudstones, schists, limestones and others can explode when heated to high temperatures! I wouldn't recommend doing this.
I appreciate the warning. It was the first thing that crossed my mind when i thought about doing it. I have some other projects going that need to be heated so these will probably see a 200F oven to 6-8 hours then a 400F oven before they see the kiln. I don't want anything turning to ceramic either so i won't be going too high. Outdoor project for sure.
 
@musicman980 it'd be kinda cool if it vitrified like an india.i would be down to learn how to make homemade India stones. Id make one with powdered novaculite but not bake it too hot so it'll be friable. A man made washita of sorts.
 
Curious what vitrification temperatures would do to the crystalline structure of novaculite?
Looked back at honing and grinding part 3. The stone they experiment on is Burnt Eidsborg. They use temperatures starting at 400C~750F to 1100C~2000F. They only comment on the hardness of the stone after heating not any other properties. Doubt i will be going to 1100C because, as @musicman980 pointed out, they can explode at high temperatures. I would prefer not to find out at what temperature Pennsylvania blue stone explodes.
 
Here is a piece I just sealed in a batch of stones. It’s hard, and there were a few cracks in the sides that needed sealing with CA before the spar urethane. One of the cracks was sizable and part of it went up across the layers. I thought a slate would split along the layers, so perhaps this is a hard shale. 210 x 60 x 36

I worked up a slurry with a worn atoma 400 and worked that slurry for a while, very slowly diluting it and actually finishing on a thicker slurry than I normally would (compared to a jnat finishing slurry). The shave test will have to wait for a few days.

The point of all of this isn’t so much to find the best razor honing material in existence, or start a hole mining operation. There are a lot of legendary razor hones out there with established reputations. These past few years of rock hunting were a part of a switch in mindset - moving further away from mass production and into local goods and services. At the end of the day I feel better eating a meal with locally grown food, on a plate made by the local potter, at a table I made myself from local wood. Even finding a single rock that can do the job would be amazing, because then they become tools again. This isn’t a flashy Nakayama maruka kiita sports car that I bought just to show it off, this is a rock fine enough to finish a razor, and I found it at the creek.


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I had a really nice shave off of this hard shale yesterday. The edge was quite comfortable, but not scary sharp. I finished with more slurry than I normally would, so I think there is room for improvement.

Slates have a more consistent grain than shales, but shales can potentially have a finer grain size than slates. This is due to the metamorphism that creates the slate - more compression creates a harder and more consistent rock, but that same compression compresses smaller particles together into bigger particles. Harder stones can give the impression of superfineness because the grit stays locked in the stone, but I think the best razor hones are the superfine, hard, and consistent shales. They are MUCH harder to find in my experience.

I don't usually see jnats split into large, clean and crisp foliations like a typical commercially mined slate, so perhaps they are more on the hard shale end of the spectrum. Does anyone know for sure where jnats lie on the sedimentary rock spectrum?
 
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