Natural Sharpening Sandstones

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cotedupy

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(A follow up to my universally-admired post about slate).

Unlike slate, sandstone is a sedimentary rock. It has not been transformed by heat and pressure into something new; it is simply compressed sand held together by other stuff, or ‘lithified’ if we want to get technical. But like slate, sandstone has also been used for thousands of years to make things sharper.

This again of course, is because of quartz (gets everywhere eh) - sand, generally, is mostly quartz. Though they might normally be rather larger bits of quartz than we’d find in other whetstones, which would make them particularly suited for grinding, or coarser sharpening work. You can get finer sandstones, just usually they’re coarser.

A month or so ago I found a sandstone that I thought had some potential. I could tell instantly that it was a sandstone because I found it on the beach. (Joke - I have no idea if it’s a sandstone, I think it probably is, but anyone feel free to correct me). It’s quite pretty, got layers n stuff:

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And the particles appeared to be very evenly distributed and sized, this is difficult to get a picture of but to my eye the whole thing is basically made from twinkly little bits of sand/quartz:

IMG-3636.JPG


This evening I thought I’d try it out… going by my tried and tested ‘Tooth Method’ this seemed like it’d be about 800 grit, if it worked at all. Even with Mr. 40-Grit-Sanding-Belt and Little Miss 140-Atoma that wasn’t the easiest of tasks, and took a wee while, but we got there in the end. It isn’t perfect, but enough of it is flat enough for us to try it out:

IMG-3628 (1).JPG


We’ll be using a cheap Bunka blade that I’ve vinegar-ed the rust off, and which has not a snowflake’s chance in hell of going through any kind of paper:

IMG-3632.jpg


The stone is hard, it does not slurry easily, and again takes a bit of effort with a diamond plate to get here, which I think looks ok for a working mud:

IMG-3639.jpg


Now I obviously wasn’t going to bother typing all this out just to say at the end that it was a piece of cr*p which I should’ve left on the beach. So yeah - the stone works well. It’s probably a little finer than my initial guess, maybe around 1k, and it feels nice-ish to use, though not a massive amount of 'feedback'. After maybe five mins or so our Bunka goes easily through newspaper, and will have a fair crack at kitchen towel, though not all cuts were as clean as this:

IMG-3640.jpg


In summary - I was pretty pleased with it tbh. I’ve had some practice in looking for and using stones, so I was hoping it’d be ok, but it’s the first time I’ve tried or used a sandstone, so really I had no idea. It’s obviously not as quick as a synthetic stone, nor as easy to use, but it’s actually not far off the former - this didn't take long, and it works perfectly well. A fun thing to have!

Lastly- there was one aspect in particular that made me wonder… I assume in a sandstone we’d probably want the bind to be quite hard / solid, otherwise you’re just going to get a load of bits of scratchy sand being released the whole time. But this seems very hard indeed; it feels like sharpening on something quite smooth, and is not really releasing any particles at all afaics. It seems the sharpening is being done solely on what’s in the stone itself rather than the mud I’d raised. Will this mean at some point we’ll just round out, or blunt, the abrasive quality of the quartz in the stone? Or does lapping / slurrying with a diamond plate obviate that problem?

And if anyone wants to have a look at it properly and tell me it’s clearly not a sandstone, and that I’m a complete idiot, here ya go: https://drive.google.com/file/d/13_I32sk3xRxarEdmG6xeAp7kY3wS0Rzz/view?usp=sharing
 
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Luftmensch

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Fun adventures! 😎



But this seems very hard indeed; it feels like sharpening on something quite smooth, and is not really releasing any particles at all afaic
That one does look hard! Sounds even harder than an Amakusa/Binsui. Although these sound like they self slurry more?

It seems the sharpening is being done solely on what’s in the stone itself rather than the mud I’d raised. Will this mean at some point we’ll just round out, or blunt, the abrasive quality of the quartz in the stone? Or does lapping / slurrying with a diamond plate obviate that problem?
Possibly? If it doesnt raise much mud then it is likely you are predominantly removing steel from the abrasives embedded in the stone surface. As they wear out or round over, the stone will slow down and act finer. Lapping with a diamond plate will refresh the surface and expose 'new' abrasives - you don't need to do too much. Just enough to remove the worn out surface. Depending on your stone, patience and objectives, you might want to do that every 30-60 seconds.... or.... maybe once per bevel side is sufficient.


Cool stuff!
 

cotedupy

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Fun adventures! 😎





That one does look hard! Sounds even harder than an Amakusa/Binsui. Although these sound like they self slurry more?



Possibly? If it doesnt raise much mud then it is likely you are predominantly removing steel from the abrasives embedded in the stone surface. As they wear out or round over, the stone will slow down and act finer. Lapping with a diamond plate will refresh the surface and expose 'new' abrasives - you don't need to do too much. Just enough to remove the worn out surface. Depending on your stone, patience and objectives, you might want to do that every 30-60 seconds.... or.... maybe once per bevel side is sufficient.


Cool stuff!
I've actually got a Morihei Binsui that I reckon is probably around the same level of effective grit, so might have to try them out side by side, and report back...

Thank you for the lapping advice too - I wouldn't have thought to do it little and often, but makes sense - will try that out too.

And yep... even though I'll rarely use this stone for any normal sharpening I don't think, it's still quite a fun way to learn about different abrasives, and the characteristics of natural stones :).
 

Luftmensch

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Lots of fun!

I wonder how well a tomo nagura would work for refreshing the surface? I haven't tried too many naguras... I did experiment a little by using 240 SiC power on my Amakusa... it was hoping I would have the hardness of a natural stone with the cutting speed of a synthetic... I suppose it worked... for a minute or two. It was weird! A crunchy experience that seemed to generate slurry (work on the stone) quicker than it removed steel 🤪

I have this unsophisticated view of regarding coarse stones as 'base' preparation stones. Stones for only heavy bevel work (removing chips and super dull edges) or thinning. Naturals do not excel at this... But I am coming around a bit (in part thanks to @captaincaed's HHT thread). 'Coarse' stones can be used much more subtly. A lighter touch and patience can get very sharp results - I actually think hard stones that don't release too much grit can be an asset in this regard. As you work the stone they shift from being coarse to fine and possibly even burnishing.... You can control that by how often you keep the surface abrasives fresh.
 

cotedupy

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Lots of fun!

I wonder how well a tomo nagura would work for refreshing the surface? I haven't tried too many naguras... I did experiment a little by using 240 SiC power on my Amakusa... it was hoping I would have the hardness of a natural stone with the cutting speed of a synthetic... I suppose it worked... for a minute or two. It was weird! A crunchy experience that seemed to generate slurry (work on the stone) quicker than it removed steel 🤪

I have this unsophisticated view of regarding coarse stones as 'base' preparation stones. Stones for only heavy bevel work (removing chips and super dull edges) or thinning. Naturals do not excel at this... But I am coming around a bit (in part thanks to @captaincaed's HHT thread). 'Coarse' stones can be used much more subtly. A lighter touch and patience can get very sharp results - I actually think hard stones that don't release too much grit can be an asset in this regard. As you work the stone they shift from being coarse to fine and possibly even burnishing.... You can control that by how often you keep the surface abrasives fresh.
Well you'll certainly have far more experience than I do with nagura anyway! I only have a cheap King one, and I don't use it much at all tbh... maybe that's the next weird rabbit-hole I'll fall into... ;)

I've been playing around with some of my coarser stones recently to try out that kind of thing. It's quite satisfying when you get to understanding a coarse stone (or indeed random bit of rock) well enough to use it to take a knife through to very sharp.

And for exactly the reason you said - I keep a lot of sanding belts and sheets at different levels of wear, rather than chucking them out. I can make a handle really quite shiny on a completely worn 80 grit belt, and used 2k sandpaper is incredibly good for buffing horn ferrules n stuff :)
 

Desert Rat

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I have not found a local source of sandstone suitable for honing of any kind, it's just to crumbly. I do use the Hindostan and also the Berea grit grindstones. There a a couple others that I have been wanting to try though.
 

VICTOR J CREAZZI

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Here in Colorado and Wyoming there is a deposit of Dakota sandstone that is exposed in a hog back for literally hundreds of miles. I've seen several old treadle powered wheels that appear to be made of sandstone from this formation. My experience with it is that it is coarse and slow as a sharpening stone.
 

cotedupy

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I have not found a local source of sandstone suitable for honing of any kind, it's just to crumbly. I do use the Hindostan and also the Berea grit grindstones. There a a couple others that I have been wanting to try though.
That's exactly the reason I wasn't quite sure about what this was. I think it is a sandstone, but it's the opposite to that kind of quite crumbly type that I'd also be used to. I guess there are all sorts of different variations though... (?)
 

cotedupy

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There has to be a continuum from sandstone on its way to quartzite.
This is probably a very good point I imagine. I shall have to try to read up a bit more.

I did just come across this paragraph from Henk B:

'Sometimes I was asked why I look so extensively to the fracture surface of a sandstone. This is due to the influence of silicic acid on the binding of the quartz grains. Silica namely produces rock solid sandstone. This can be seen on the fracture surface. When knocking off a piece of rock the fracture goes through the grains, the rock is so hard that we are dealing with a non-metamorphic quartzite. The northern sandstones are often kwartsitis. Due to the hardness of the binding (matrix) these stones are not suitable for grinding. When the grains namely get blunt they will not break out of the matrix and the grinding effect stops.'

This sounds like it might be how my stone ends up tbh. It may prove more trouble than it's worth in the long run. But I'm going to give it a bit more flattening and proper testing to see.
 

Desert Rat

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I have a Norton Queer Creek stone I use on some axes I have. The stones, like this one, are readily available and inexpensive. May be worth a try if you find one locally. They are sandstone.
I suspect that it is the same stone that Norton now sells under the Clear Creek label, but I'm not positive on that.
 

cotedupy

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That one does look hard! Sounds even harder than an Amakusa/Binsui. Although these sound like they self slurry more?



Possibly? If it doesnt raise much mud then it is likely you are predominantly removing steel from the abrasives embedded in the stone surface. As they wear out or round over, the stone will slow down and act finer. Lapping with a diamond plate will refresh the surface and expose 'new' abrasives - you don't need to do too much. Just enough to remove the worn out surface. Depending on your stone, patience and objectives, you might want to do that every 30-60 seconds.... or.... maybe once per bevel side is sufficient.


Cool stuff!
I did end up trying it next to my Binsui btw the way a little while back... The Binsui feels much scratchier and less even, though I guess they're probably roughly the same in terms of grit, maybe the sandstone is marginally finer.

Though the Binsui doesn't slurry much, the sandstone is notably harder. In terms of sharpening they're pretty similar speeds; not very fast, but not horrifically slow. The sandstone is better though, the edge is finer, and sharper than the Binsui.

This was only the second time I've used it properly, so still don't really know how often it'd need to be lapped to keep it cutting well. I suspect it'd need a little bit of atoma 140 action every time, so probably not really going to be a regular-use thing. Just fun to have around.

IMG-1165.jpg
 
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