# Natural Sharpening Slates



## cotedupy (Mar 14, 2021)

Now there will be a lot of people here with more experience that I have when it comes to using slates, especially those in the straight razor game. But I thought I'd do a little post for anyone who might be interested in going out and finding their own stones. Much of the information, and all quotes, in this come from Henk Bos's fascinating studies / papers concerning European natural sharpening stones, which I will link to at the end. Accented by some of my own experiences - I live quite close to some of the oldest slate quarries in Australia at Willunga, and have easy access to a good amount of it for free.

Slate is 'An indispensable natural abrasive... In almost every country are slate whetstones made.' It is a layered metamorphic rock; largely mud that has been compressed and transformed by heat and pressure. And mud, compressed or otherwise, is not necessarily the best thing to sharpen knives with. Why then have slates been used for thousands of years as whetstones?

'Slate for a whetstone or grinding stone is a slate with small particles of a quartz variety. If these quartz particles are extremely minute and uniform in size and has the correct hardness of the bond, it is suitable for whetstones of the best quality.'

When I pick up a stone I will first check for evenness using either a fingernail, or my teeth, and perhaps one stone in 20 I will take home. A stone off the ground is obviously rather grubby, randomly shaped, and not flat. I use a mallet to break them slightly into more suitable sizes, and then do an initial flattening on a belt sander. Mask time! Slate dust is particularly nasty.







After that I use a diamond plate for proper flattening, and then test the stones out. Here are some I've tried recently, bearing in mind that these were selected out of maybe 150 stones:











Of these - no.s 2, 3, 5, & 11 are not so good - there's a heterogeneity to the particles that'll cause problems for us. Here is as good a picture of what I mean as I could take, in stone 2:






The eagle-eyed will notice that stone 6 has a *markedly* different coloured mud from the others. There are incursions in this stone from something which is muddier, coarser, and greener. A very different stone to the others. I will probably not persevere with this one.

The unpictured stone 7 I've had for a while and know it's good, so didn't bother trying again.

Stones 1, 4, and 10, are similar to 7; these are what I'd consider as typical good Willunga slate whetstones. They are hard, quite fine, but even. They have little cutting power and raising slurry is difficult; I tend to do it with water and a diamond plate. I've tried with oil, as you might use an Arkansas, but I don't have enough experience with that, so prefer water. Here's an example of mud on (I think) stone 1:






And here's stone 1 when pretty much properly flattened and ready to roll:






I also don't really have much experience rating the grit of natural stones, but at a very random guess these might be 2-5k depending on how they're used. The edge they leave is _very _refined, I've found them most useful in a progression before going back to a stone that leaves a more bite-y edge to finish. Having said that... after (a fair bit of) practice I can use a single one of these stones to sharpen a knife very well. They work nicely; it just takes a while.

A lot of these stones I'll be giving away to people, and when I ask if they'd like a finer or coarser one, they almost always answer: 'finer'. But as we know - a fine slate is largely just compressed mud. And it's feckin' difficult to use tbh.

Stone 8 is our Goldilocks stone:






It slurries easily, and cuts well. This is the stone that really best has those minute and even particles of quartz in it, wot we wanted originally.

This is a petty I purposefully made very blunt and then sharpened using just stone 8. It took about 5 mins: https://drive.google.com/file/d/1iH-tnSbFApCsOfCQZDNdD1aplVzNUr3V/view?usp=sharing

And that's the end of my long and probably quite boring post about slate!


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## cotedupy (Mar 14, 2021)

Henk Bos's studies: Different Types of Natural Stones


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## Rangen (Mar 14, 2021)

Fascinating post! Thank you.



cotedupy said:


> When I pick up a stone I will first check for evenness using either a fingernail, or my teeth



Except for this part. This part is scary. How many teeth do you have left now?


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## HumbleHomeCook (Mar 14, 2021)

cotedupy said:


> Now there will be a lot of people here with more experience that I have when it comes to using slates, especially those in the straight razor game. But I thought I'd do a little post for anyone who might be interested in going out and finding their own stones. Much of the information, and all quotes, in this come from Henk Bos's fascinating studies / papers concerning European natural sharpening stones, which I will link to at the end. Accented by some of my own experiences - I live quite close to some of the oldest slate quarries in Australia at Willunga, and have easy access to a good amount of it for free.
> 
> Slate is 'An indispensable natural abrasive... In almost every country are slate whetstones made.' It is a layered metamorphic rock; largely mud that has been compressed and transformed by heat and pressure. And mud, compressed or otherwise, is not necessarily the best thing to sharpen knives with. Why then have slates been used for thousands of years as whetstones?
> 
> ...



I think it was a great post. Thanks for taking the time!


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## cotedupy (Mar 15, 2021)

Rangen said:


> Fascinating post! Thank you.
> 
> 
> 
> Except for this part. This part is scary. How many teeth do you have left now?




Cheers!

Haha... Yeah perhaps I shouldn't do it too much. It's just much easier to _hear_ the consistency of the grain when using your teeth, than _feel_ it on your fingernail.


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## cotedupy (Mar 15, 2021)

HumbleHomeCook said:


> I think it was a great post. Thanks for taking the time!



Ta!


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## cotedupy (Mar 15, 2021)

A shout out to @KingShapton who suggested I pay particular attention to the look of stones that I thought good... I was using stone 8 again last night and noticed something interesting. In the video below the stone is completely flat and clean. The wavy patterns I assume show that we're actually sharpening across some very fine layers within the stone, which is something I've heard suggested before. This was very much more by luck than design.

It's slightly difficult to capture in vid/pics, but actually rather beautiful.



https://drive.google.com/file/d/1mlra3GzOSmpjyfB8_N1Gm8GE8ssTLKZ2/view?usp=sharing


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## captaincaed (Mar 16, 2021)

Very cool experiments


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## cotedupy (Mar 18, 2021)

And a final update...

Stone 1 gave to another forumite and just got some very +ve feedback. Which has reassured me somewhat that I'm not going crazy, and that Willunga slate is actually quite good for sharpening. He even used it for some pretty natty polishing/kasumi.

Of the rest; stones 4, 7, 8, 9, and 10 I have properly flattened and used and are good. Pictured here in order:






4 & 7 slurry nicely, and have good grain. We don't have any scratchy bits, but they're not completely homogenous. They're going to be very good stones for sharpening.

8 you'll remember was our 'Goldilocks' stone. I've used this a fair amount now, and it's lovely. It compares happily with the best stones I have. It's also _beautiful._ Here is a highly stylised picture of stone 8:






9 & 10 are different from the others. Harder and more difficult to slurry, and 10 in particular I think is an excellent stone. But they're very similar, and after using them properly - I think they're probably actually from the same piece:






And for anybody who has struggled all the way through this thread but is still, for some reason, wanting more... here's a poorly-shot sharpening video I made this afternoon on my old iphone about how I use them: https://drive.google.com/file/d/1RlJQNyJrPctsHARhCLiScvSUbDWS83R5/view?usp=sharing


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## RDalman (Mar 18, 2021)

Nice writeup! I break out my swedish slate Los-hone sometimes, good toothy finisher, they tested them to ~1500 grit but feels finer. Also have a "belgian blue" which is supposed to be ~4k, but I don’t fancy that one for some reason, maybe too slow just.


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## captaincaed (Mar 18, 2021)

The Belgian blue doesn't seem to leave a very toothy edge for me. Seems like a good mid point for a razor, but doesn't always shine in the kitchen. It does cut pretty quickly for me if I raise slurry with a lapping plate. 

My translucent Ark cuts very quickly with a slurry from a diamond plate. But RIP diamond plate after that trick...


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## captaincaed (Mar 18, 2021)

Robin, you gotta take a break from the forum and go on vacation!


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## RDalman (Mar 18, 2021)

captaincaed said:


> Robin, you gotta take a break from the forum and go on vacation!


Hey I can't get out of the recliner after two days of laying floor! Body well broken down, like all new muscles that got to work. A cold one and Kkf it is


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## captaincaed (Mar 18, 2021)

Haha! You do you!

....
In Mother Sweden, we bring the nature inside...


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## RDalman (Mar 18, 2021)

captaincaed said:


> Haha! You do you!
> 
> ....
> In Mother Sweden, we bring the nature inside...


Haha the kid got jealous of my hammering so she wanted some nail-hammering action on the livingroom carving/chopping block


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## captaincaed (Mar 18, 2021)

RDalman said:


> the livingroom carving/chopping block


You're going to say this totally casually?!
....you Swedes aren't normal, you know that?


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## RDalman (Mar 18, 2021)

captaincaed said:


> You're going to say this totally casually?!
> ....you Swedes aren't normal, you know that?


My gf tried to argue but it was about my one non-negotiable thing I wanted to have when moving to house. I did let her argue the purdy hardness tester away from the living room to bedroom


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## captaincaed (Mar 18, 2021)

I'm all out of words.


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## Rangen (Mar 18, 2021)

RDalman said:


> My gf tried to argue but it was about my one non-negotiable thing I wanted to have when moving to house. I did let her argue the purdy hardness tester away from the living room to bedroom



You rock, sir.


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## cotedupy (Mar 18, 2021)

captaincaed said:


> You're going to say this totally casually?!
> ....you Swedes aren't normal, you know that?



I salute you RD... living the dream!


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## cotedupy (Mar 18, 2021)

RDalman said:


> Nice writeup! I break out my swedish slate Los-hone sometimes, good toothy finisher, they tested them to ~1500 grit but feels finer. Also have a "belgian blue" which is supposed to be ~4k, but I don’t fancy that one for some reason, maybe too slow just.



Ta! Yeah all this has made me rather interested in trying others. Lots of potential I think - some of these are really excellent stones. There's also at Willunga... '_Australia's Only Slate Museum', _which I am unreasonably excited about going to visit soon.


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## cotedupy (Mar 18, 2021)

captaincaed said:


> The Belgian blue doesn't seem to leave a very toothy edge for me. Seems like a good mid point for a razor, but doesn't always shine in the kitchen. It does cut pretty quickly for me if I raise slurry with a lapping plate.
> 
> My translucent Ark cuts very quickly with a slurry from a diamond plate. But RIP diamond plate after that trick...



Forgive me a probably very basic q. but... why has your translucent Ark killed a diamond plate? Surely they can't be that hard?! (I've never used or seen an Arkansas, so know very little about them).


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## captaincaed (Mar 18, 2021)

They're super hard quartz, no binder. The plate still works, but it took a bad hit. A coarse waterstone will do the same.


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## cotedupy (Mar 19, 2021)

captaincaed said:


> They're super hard quartz, no binder. The plate still works, but it took a bad hit. A coarse waterstone will do the same.



Ah... interesante!

I've noticed that the 400 side of my plate has been taken down a bit by all this. But now that I have a 140 as well - I actually quite like the slightly smoother version of the 400 for slurry, and can use the 140 for flattening


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## captaincaed (Mar 19, 2021)

Yeah once they're worn they're great for slurrying


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## DavidPF (Mar 19, 2021)

cotedupy said:


> '_Australia's Only Slate Museum'_


It might be hard to calculate the optimum number of slate museums for Australia.


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## cotedupy (Mar 20, 2021)

DavidPF said:


> It might be hard to calculate the optimum number of slate museums for Australia.



A perceptive comment I think. And you are of course correct... it would impossible for the human mind even to conceive of any country that might have _too many _slate museums. The very idea is absurd!

I'm off to visit tomorrow


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## DavidPF (Mar 20, 2021)

cotedupy said:


> it would impossible for the human mind even to conceive of any country that might have _too many _slate museums. The very idea is absurd!


The Welsh are with you all the way. The Libyans appear slightly puzzled and are requesting clarification.


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## Luftmensch (Mar 20, 2021)

@cotedupy 


Awesome post... I think you had a similar one on forming some slate stone into a whetstone? I had a little (rainy) beach sanity holiday a couple of weekends back. We walked past some slate. Inspired by the post I decided to fossick about for some slate to cut. I found two imperfect pieces - it would have been fun to make an afternoon of it. I'll post some photos at some point.

I would guess mine are somewhere around the 800-1000 mark. It was a fun exercise but I am not sure they are practical stones. They are literally very muddy stones . I would guess they are coarse-ish granules of quarts pressed into a fine silt - so I am not getting the benefit of either a coarse stone nor a fine stone. It is slow for a coarse stone and coarse for a fine stone


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## cotedupy (Mar 20, 2021)

Luftmensch said:


> @cotedupy
> 
> 
> Awesome post... I think you had a similar one on forming some slate stone into a whetstone? I had a little (rainy) beach sanity holiday a couple of weekends back. We walked past some slate. Inspired by the post I decided to fossick about for some slate to cut. I found two imperfect pieces - it would have been fun to make an afternoon of it. I'll post some photos at some point.
> ...



Ah cheers!

Yep... I did a post I think about 6 months ago (?) asking some questions when I first found and tried one out. TBH I've also not had a massive amount of luck with ones that I've found on the ground round here - most of these have come from the quarry at Willunga (about 15 mins away). My in-laws apparently bought a load of it to use as paving stones for the garden at their farm, and pieces that got rejected for paving they kinda left in little piles around the place. Which is why it takes me very little time to find stones - I'm mostly just looking through those piles at their farm. And the ones that aren't good for paving or walls tend, conveniently, to be whetstone-ish size 

You're in Aus right...? Ping me a message if you'd like to try one (free - just the cost of postage). I'm certainly quite interested in hearing what other people with more experience than me think of them...


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## Luftmensch (Mar 20, 2021)

Interesting!

Hehe... I thought you might have gone into the hills and found some suitable rocks 

I was on a walk by the ocean and passed some slate. Your older thread popped into mind and I rather opportunistically decided to stop and take two whetstone-sized pieces home. I didn't really have time to choose the 'perfect' stone (it was raining!). So I never expected the stones to be anything more than functional.

I am an Aussie (NSW)! The stone is from the mid-north coast of NSW - so about 1500km away! In someways it is a very 'marine' stone... that coarseness I talked about has a sandy quality to it... but finer. After a bit of Googling, it looks like the stone is likely to be a mica-quartz slate - nothing fancy like garnets.

It was neither a failure nor a success... just a fun distraction i suppose! I like the idea of trying to find an Ozzie natural. If only I had a geologist friend to recommend some good local hunting grounds!


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## cotedupy (Mar 20, 2021)

Yeah I think the quarried ones are going to be quartz, though they sound finer and more even. (You can't see the bits in them for instance). The ones that I've gone and picked up nearby from slate outcrops are more like yours I imagine.

Anyhow, I shall know much more this time tomorrow. Whoever's writing the website copy certainly knows how to play to their target market... I am _tantalised_!!!!


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## cotedupy (Mar 20, 2021)

Though slightly disappointed by the size of it. Perhaps there's another building behind.


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## Luftmensch (Mar 20, 2021)

cotedupy said:


> Yeah I think the quarried ones are going to be quartz, though they sound finer and more even. (You can't see the bits in them for instance). The ones that I've gone and picked up nearby from slate outcrops are more like yours I imagine.
> 
> Anyhow, I shall know much more this time tomorrow. Whoever's writing the website copy certainly knows how to play to their target market... I am _tantalised_!!!!
> 
> View attachment 119369



That is hilarious!! Six words... and four of them are slate. You're right, they do know how to play to their target market. Let us know how it goes!

Mine are not uniform at all... pretty... but thats about it  Yours look better for grit uniformity.


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## DavidPF (Mar 20, 2021)

cotedupy said:


> Though slightly disappointed by the size of it. Perhaps there's another building behind.


Remember the website. How much indoor space does it take to write "Look - Slate!" 

I guess they could put a helpful sign beside the window:

← (this bit is not slate)


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## cotedupy (Mar 20, 2021)

They had me at 'Slate...' to be honest.

I shall of course endeavour to find out which renowned expert or pioneer it is that they are quoting.


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## DavidPF (Mar 21, 2021)

cotedupy said:


> which renowned expert or pioneer it is that they are quoting


From etymonline:


> from Old French esclat "split piece, chip, splinter" (Modern French éclat), back-formation from esclater "to break, splinter, burst," probably from Frankish *slaitan "to tear, slit" or some other Germanic source (compare Old High German slizan, Old English slitan...)


Slate and slat are extremely near being the same word, not just because they look similar but because they used to mean the same thing, and originally came from the idea of splitting off pieces of something.

Hopefully that satisfies the scholarly pursuit. 

Speaking of pursuits, people who go looking for birds are sometimes called birders. Maybe now you're a stoner.


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## cotedupy (Mar 21, 2021)

DavidPF said:


> From etymonline:
> 
> Slate and slat are extremely near being the same word, not just because they look similar but because they used to mean the same thing, and originally came from the idea of splitting off pieces of something.
> 
> ...



I didn't know that! EtymologyOnline sounds like a splendid website, I shall remember it 

Alas it seems that my faith in the information on the Willunga Slate Museum's website was misplaced. And there is little call for it to be open _every _Sunday - just one Sunday each month now apparently.

No more does the cry of "Slate! Slate!! SLATE!!!" (so familiar to our forebears) ring out across the McLaren Vale. Sad times indeed.


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## cotedupy (Mar 24, 2021)

So I was quite pleased with myself here...

When I try out a new stone I usually trash up the edge of a knife and make it really very blunt, then see how it sharpens using just that stone. I could tell stone 13 was gonna be pretty good, but feckin hell! It took about 10 mins of sharpening to go from incredibly blunt to HTT cutting (which is not something I ever get to normally on any stone tbh).


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## KingShapton (Mar 24, 2021)

Goldilocks stone!


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## cotedupy (Mar 24, 2021)

KingShapton said:


> Goldilocks stone!



I was flabbergasted. I occasionally try it if I think I've made a knife particularly sharp, and it barely ever works. But doing it just using a stone off the ground has surely got to earn me some kudos with the cool kidz on the sharpening forum


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## cotedupy (Mar 30, 2021)

Yesterday another forum member (knowing my weird interest in slate) very kindly gave me a Chinese stone, which he thought might be a kind of slate. And having tried it out quickly last night - it certainly is. It's not an expensive stone, but actually I quite like it. However it does show the problems I mentioned that can happen with inclusions in a stone that have a rougher, less uniform grit. Though the binding agent in this stone is seemingly a little harder than Willunga slate, which makes it less of a problem. 

In this picture you can see a darker area at the bottom, kinda running from my thumb to my little finger:






And here, how that darker has some bigger quartz particles that kinda catch the light, but the lighter area doesn't:






Apologies for the grainy indoor nighttime pics. Until fairly recently I might've looked at the black marble surface in a hotel toilet and thought something other than: '_Oh that looks nice and flat... it will be perfect for trying out a new stone.'_


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## KingShapton (Mar 31, 2021)

Is the stone one of the so called "chinese 12k"?


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## cotedupy (Mar 31, 2021)

KingShapton said:


> Is the stone one of the so called "chinese 12k"?



I don't think so; not sure what, if any, packaging it came with. And it's certainly not anything like that grit - I'd guess the main part is around 2-3k. It was a very inexpensive one from a Chinese kitchenware store, which actually isn't too far from where I'm staying so I'll probably go along this afternoon. What are the odds I come away with another cleaver...? 

I'm starting to really quite like slates for sharpening, they seem much gentler on steel than my other stones, but can still get results.


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## cotedupy (Apr 1, 2021)

Did I manage to leave without buying a caidao? Did I feck! They turned out to have a load of CCKs behind the counter inc. what is probably about my favourite size - 1302. At $67 US equivalent it seemed a pretty decent price


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## ModRQC (Apr 1, 2021)

Hell of an experimental report! Amazing work thank you for the thorough presentation. Goldilocks makes me want to lend her my chair, bowl and bed to sleep on. Have you made some experiments in polishing with the good ones?



cotedupy said:


> View attachment 119928



You have me curious there, especially with your testing stones with your teeth... what's the spoon for then?


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## ModRQC (Apr 1, 2021)

Ah... to match Goldie's borrowed bowl, surely.


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## cotedupy (Apr 1, 2021)

ModRQC said:


> Hell of an experimental report! Amazing work thank you for the thorough presentation. Goldilocks makes me want to lend her my chair, bowl and bed to sleep on. Have you made some experiments in polishing with the good ones?
> 
> 
> 
> You have me curious there, especially with your testing stones with your teeth... what's the spoon for then?



Ta!

Yeah... I only learnt about the spoon thing recently after getting these stones. It's definitely a test I'll try out next time, before I grind my teeth away 

And yep - 'Goldilocks' as is in neither too muddy, nor too hard. And grain not too large, nor too small. Maybe I could also call it a 'Mary Poppins' stone... practically perfect in every way!

I've not done too much polishing with them, although someone I gave one to recently managed quite nicely. So I tried out again, and they it was actually quite good. I may have a proper go on stone 8 this evening and see how it comes up... (with the caveat that I am no expert at all with that kind've thing!)


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## ModRQC (Apr 1, 2021)

cotedupy said:


> Ta!
> 
> Yeah... I only learnt about the spoon thing recently after getting these stones. It's definitely a test I'll try out next time, before I grind my teeth away
> 
> ...



I’m sure you’ll manage quite fine. Would make a nice add-on to this great presentation. I’d like to see for sure, mud seems promising on the better units.


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## ModRQC (Apr 1, 2021)

Ah... if only one thing, polishing will greatly help you assess the grit range of them. From the HTT test edge as pictured, although light may be misleading, I would assess related Goldilocks edge bevel tone 1.5-3K grit range.


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## cotedupy (Apr 1, 2021)

ModRQC said:


> Ah... if only one thing, polishing will greatly help you assess the grit range of them. From the HTT test edge as pictured, although light may be misleading, I would assess related Goldilocks edge bevel tone 1.5-3K grit range.



Ha... That's very kind, but I think you may be grossly over-estimating my sharpening abilities to think I'd be cutting hairs at 3k! (I've never managed on any of of my synthetic 3ks anyway).

I tried out a bit of polishing / kasumi this eve, and I'm still not sure I quite like it. As I say - this is something I know f-all about, so maybe I'll learn and practice a bit more and do a proper additional post sometime later.






It does however make a knife really quite sharp. Nice clean cuts through kitchen towel:






And a sharpness test I saw Mr @Kippington use the other day, so thought I'd try myself (note the expert stropping on my rock-hard biceps ):

https://drive.google.com/file/d/1gJxtTwuKx79fSR_MtxszGpmdX4deMjkB/view?usp=sharing


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## ModRQC (Apr 1, 2021)

Lolz! 

I don't really care about the hair, or how good you sharpen. It can't "prove" anything to me.

I was just going from the bevel tone - and now your polishing progression. Again, this to me looks like something between 1.5K and 3K. Just as the edge bevel tone is dullish rather than mirror-ish. 

Of course I wouldn't know with slates, it may translate differently. And of course, mine eye conditioned with stones I tried, far from absolute coverage of all kinds.

It's really cool that you did all of this to show us. I think your few Goldilocks are nice ones, you should be proud you went through the process of identifying your best pieces like that.


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## Desert Rat (Apr 1, 2021)

cotedupy said:


> Yesterday another forum member (knowing my weird interest in slate) very kindly gave me a Chinese stone, which he thought might be a kind of slate. And having tried it out quickly last night - it certainly is. It's not an expensive stone, but actually I quite like it. However it does show the problems I mentioned that can happen with inclusions in a stone that have a rougher, less uniform grit. Though the binding agent in this stone is seemingly a little harder than Willunga slate, which makes it less of a problem.
> 
> In this picture you can see a darker area at the bottom, kinda running from my thumb to my little finger:
> 
> ...


The shiny particles in slate is mica, its soft. It does seem to me that that my finer slates have smaller mica particles.


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## cotedupy (Apr 1, 2021)

Desert Rat said:


> The shiny particles in slate is mica, its soft. It does seem to me that that my finer slates have smaller mica particles.



Oh really? Happy to be corrected, but from what I've read, particularly in these two papers, gave me the impression it was most likely to be quartz. (Though some slates do also contain mica).



https://bosq.home.xs4all.nl/info%2020m/grinding_and_honing_part_3.pdf




https://bosq.home.xs4all.nl/info%2020m/grinding_and_honing_part_2.pdf


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## Luftmensch (Apr 1, 2021)

For my slate:



Luftmensch said:


> After a bit of Googling, it looks like the stone is likely to be a mica-quartz slate



(I found an academic paper on the geology of the region)



On my slate, I cant say which is which... but I am guessing the mica causes the glittery shimmer in my stone. It is super subtle, beautiful and hard to capture on camera! I would guess the quartz is responsible for the larger, more granular and glass-like particles.

By referring to the oracle, mica doesnt look like a particularly useful 'abrasive'


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## cotedupy (Apr 2, 2021)

Luftmensch said:


> For my slate:
> 
> 
> 
> ...



This sounds quite plausible, I think. I know the kind of thing you mean with the mica. A couple if my stones have had parts like that. Where the ones I mentioned above seem harder.


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## cotedupy (Apr 2, 2021)

ModRQC said:


> Lolz!
> 
> I don't really care about the hair, or how good you sharpen. It can't "prove" anything to me.
> 
> ...



Ah yeah I don't have much (read any) knowledge of how grit translates to polish. My guesses were based on how they feel and the edge they leave. And it changes a bit depending on how you use them.

A few other people who've tried them have thought 3-5k. And that stone 8 would probably be at the slightly coarser end of that. I've found a couple of good ones that are a bit finer. But 8 slurries and cuts better than the finer ones.


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## Desert Rat (Apr 2, 2021)

I have a small sample size of slate whetstones so I could be wrong but all of my slate stones have mica and I also use it as an identifier in unknown stones. It looks like metallic paint from the 70's. Sun light and at times magnification helps me see it.

Slate: Metamorphic Rock - Pictures, Definition & More (geology.com) 
*Composition of Slate*

Slate is composed mainly of clay minerals or micas, depending upon the degree of metamorphism to which it has been subjected. The original clay minerals in shale alter to micas with increasing levels of heat and pressure. Slate can also contain abundant quartz and small amounts of feldspar, calcite, pyrite, hematite, and other minerals.


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## cotedupy (Apr 2, 2021)

Desert Rat said:


> I have a small sample size of slate whetstones so I could be wrong but all of my slate stones have mica and I also use it as an identifier in unknown stones. It looks like metallic paint from the 70's. Sun light and at times magnification helps me see it.
> 
> Slate: Metamorphic Rock - Pictures, Definition & More (geology.com)
> *Composition of Slate*
> ...



Ah gotcha! Only a couple of my stones have that parts with that shimmery aspect that you and @Luftmensch are talking about (I didn't actually know that was mica before you guys mentioned - as you can tell I'm still very much learning!) I shall have a read of your links, cheers.

On page 10 of part 2 of the two links I put above he outlines 7 steps in the formation of slates. It sounds like your stones would be from steps 6 or 7, whereas mine are mostly from step 5, which is the first time it has become 'slate' as such, but before the formation of identifiable micas. Later in the paper he notes that it is only stones from steps 5, 6 and 7 that are suitable for whetstones.

Interesting stuff


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## cotedupy (Apr 11, 2021)

One day per month for just a few short hours the Willunga Slate Museum (the only one of its kind in Australia, don't you know) throws open its doors to the public, and reveals the treasures within... today was that day! The museum has its own eccentrically-dressed-and-bearded older gentleman, wearing a trilby, to guide you through the many exhibits. Including...

Maps n stuff, only two of the five quarries are still in operation:





Tools for breaking up slate, and tools for making tools for breaking up slate:









Info regarding the accepted SI units of slate size:





And all manner of other slate-related paraphernalia, including a Cornish Pasty in a perspex box, and a speaker that read out 19th century newspaper reports describing in 'graphic detail' the deaths of various people working at the Willunga quarries back in the day... which was an interesting touch.


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## cotedupy (Apr 11, 2021)

Also this small thing about geology, which I think probably explains relatively well what the lines or patterns are in my stone #8. It sounds like we're not sharpening across the layers of the slate as such, but rather across the original bedding planes, before the mud/shale had become slate.







Anyway, needless to say all this excitement has put me in just the mood to flatten and try out Stone 14, which is one of a few I have atm that look promising...


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## cotedupy (Apr 11, 2021)

TBH I had pretty high hopes for stone 14. It's the last one I took home that I found in the same pile as #8-13, only one of which (#11) I didn't like. To my eye it looked and felt quite like #8, but actually in use it's slightly finer, and slightly harder. More similar to #10 and #13; and the particle size/distribution is spot-on perfectly even, like those two stones. A really lovely stone to use. If I didn't owe one to @GorillaGrunt I'd be keeping this.

I was beforehand doing some thinning on a 140/400 stone, so the scratch pattern on the blade is from that, but it now happily glides through kitchen towel. And also has some great bite on the edge, which may be either because this stone actually cuts reasonably well, or perhaps because I've gone from a 400 grit stone to something around 4k... (?)


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## Desert Rat (Apr 20, 2021)

cotedupy said:


> One day per month for just a few short hours the Willunga Slate Museum (the only one of its kind in Australia, don't you know) throws open its doors to the public, and reveals the treasures within... today was that day! The museum has its own eccentrically-dressed-and-bearded older gentleman, wearing a trilby, to guide you through the many exhibits. Including...
> 
> Maps n stuff, only two of the five quarries are still in operation:
> View attachment 122230
> ...


Tools fascinate me, almost as much as the stones themselves.
On page six of this book "Ayrshire Hone-Stones", fig two shows a few tools and describes how sycthe stones where roughed out in the mine.


https://outsideecho.com/DGT-BIO_files/PDFs/DGT33.pdf



That large knife in the first picture (far right) sounds very similar to what's described here in the link provided "The Charley Forest Whetstones Leicestershire Vol2 no.4 spring 1933).








Natural stones, the Charnley Forest stone


Green and traditional woodworking. Information, advice and how too on many aspects of green wood crafts. Information on wood courses and tool sales.




seanhellman.blogspot.com





Hand cut Charnley.


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## KingShapton (Apr 20, 2021)

Desert Rat said:


> Tools fascinate me, almost as much as the stones themselves.
> On page six of this book "Ayrshire Hone-Stones", fig two shows a few tools and describes how sycthe stones where roughed out in the mine.
> 
> 
> ...


Very interesting stuff, thank you very much for sharing!


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## cotedupy (Apr 20, 2021)

Desert Rat said:


> Tools fascinate me, almost as much as the stones themselves.
> On page six of this book "Ayrshire Hone-Stones", fig two shows a few tools and describes how sycthe stones where roughed out in the mine.
> 
> 
> ...



Fascinating links, thank you. This is what the internet is for!


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## cotedupy (Apr 29, 2021)

Once more unto the breach, dear friends, once more. A closer examination of particle size, look and feel...

Outside my kitchen door I now have 3 small piles of slate. The first is slates I've found and think look promising but haven't tried. The second is pieces I've flattened and tried a bit, and then decided I wasn't so keen. The third is just chips and offcuts, that I sometimes use as slurry stones. Stone 15 and 16 are from the first pile, and Stone 3 from the second, as I thought it maybe deserved more attention. From L to R: 3, 15, 16, and 8 as a comparison.






Let's have a look at my favourite stone 8 up close (all of the following pictures of the stones have had a filter applied that maximises small bits of contrast). 8 has a _very _even particle size and distribution.






Now let's look at 3. I can't remember exactly why I wasn't so keen on it originally, but I'm 99% certain it'd be because of those brown bits on the left and the right. The middle of the stone looks a lot like 8, but those bits on the side are softer - you can see how the scratch patterns from a diamond plate are more marked there. This stone is completely flat btw.






Nevertheless, now that I've really properly flattened it Stone 3 is really quite good. It's a very lovely feeling stone; the mud from the slightly softer bits makes it rather nice to use, and it sharpens excellently. I've taken to using an old bunka blade that I trash the edge of before trying these stones. When I start on each it doesn't have a hope of going through any kind of paper, after a few mins on stone 3 it's cutting kitchen towel pretty slickly.






Stone 15 is a little different from most of the other stones I've got, and I'm not sure where I found it. But it has been cut previously by someone, and the layering is much more dense and compact than most of my other stones, barely even visible. Here's the surface of 15.






The particle size in 15 looks a bit larger perhaps, but it's quite even, and there are no really large bits anywhere (remembering that these pictures massively exaggerate differences on the surface). I re-blunt my blade and try it out... The stone is hard, it doesn't slurry much at all, and requires a fair bit of pressure when sharpening. It's not as quick as stone 3 but gets the job done after a while, the edge has a bit less bite than 3.






Something about 15 gives me the impression that it might be a good kasumi / polishing stone, so I give it a go. It's rather tricky to take good pictures of this in my kitchen at night, but there's almost no scratch pattern on the kasumi, and the edge is shiny-ish. This is the best kasumi slate I've found.






Up close stone 16 is a bit of a mess tbh. The quartz is not particularly even, and some bits are quite big:






I can't get 16 to sharpen particularly well. Unfortunately it's also relatively soft (note the atoma scratches), and releases some scratchy stuff around the place. Here's a picture of stone 16 after I've tried it out, those big glisten-y bits are causing problems. This will go off to pile 2.






I was quite happy with this evening's outcome. It's probably taught me that perhaps the hardness, or bind, of the stones has more impact on the effective 'grit' than the size of the particles... Stone 15 certainly _looks _coarser than 3 or 8, but seems to act finer, to me at least.


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## natto (May 1, 2021)

I got a old slate, might be an Escher. It came from outside in wet condition. First try was good feeling/feedback, instantly cutting. I thoght about getting me a razor. Stored dry about a decade the stone became pretty hard. 

I don't know whether soaking slates is a great idea or a no go. But I would like this process to be reversible.


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## Slim278 (Jul 2, 2021)

Here is a slate I have been playing with. Just sealed it and I think it turned out nice.


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## Luftmensch (Jul 2, 2021)

Slim278 said:


> Here is a slate I have been playing with. Just sealed it and I think it turned out nice.



Nice!! What is the 'origin story' ?


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## Slim278 (Jul 2, 2021)

Picked it up in a ditch a couple weeks ago when we were picking raspberries.


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## cotedupy (Jul 2, 2021)

Slim278 said:


> Here is a slate I have been playing with. Just sealed it and I think it turned out nice.



Nice work! Sealing is a good idea, especially for the more layered slates. I can't quite tell but yours looks to have some noticeable layering...?


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## Slim278 (Jul 3, 2021)

Yes, it has a lot of thin layers. It would not have been difficult do split it at a few of them and that was the reason for the sealing. A thick coat of fiberglass resin and no problems. I think it is easier to clean up after use as well as the top does not really absorb any water. A quick rinse in the sink and wipe with a towel and done.


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## cotedupy (Jul 3, 2021)

Slim278 said:


> Yes, it has a lot of thin layers. It would not have been difficult do split it at a few of them and that was the reason for the sealing. A thick coat of fiberglass resin and no problems. I think it is easier to clean up after use as well as the top does not really absorb any water. A quick rinse in the sink and wipe with a towel and done.



Sounds exactly like mine - water doesn't get in the top, but I have had it get in the sides of unsealed ones and cause little bits to flake off. Looks quite similar too, I imagine a nice stone, and coupled with the raspberries a pretty successful day!


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## Desert Rat (Feb 18, 2022)

cotedupy said:


> One day per month for just a few short hours the Willunga Slate Museum (the only one of its kind in Australia, don't you know) throws open its doors to the public, and reveals the treasures within... today was that day! The museum has its own eccentrically-dressed-and-bearded older gentleman, wearing a trilby, to guide you through the many exhibits. Including...
> 
> Maps n stuff, only two of the five quarries are still in operation:
> View attachment 122230
> ...


There is a slate museum in Wales also.





Story of Slate







museum.wales




*The Dinorwig Slate Quarry*


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