Natural Sharpening Slates

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Luftmensch

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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!
 

cotedupy

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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!!!!

46BD701B-FC94-4A5D-B616-2EC0DAE9DF9D.jpeg
 

Luftmensch

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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.
 

cotedupy

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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.
 

DavidPF

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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. :)
 

cotedupy

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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.

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. :)
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.
 

cotedupy

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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).

IMG_3223.jpeg


IMG_3318.jpg
 

cotedupy

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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:

IMG_3367.jpeg


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

IMG_3366.jpeg


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.'
 

cotedupy

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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.
 

cotedupy

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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 :)

C753E66D-9D82-4F50-BBA7-E06C23E00F83.jpeg
 

ModRQC

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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? :)
 

ModRQC

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

cotedupy

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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!)
 

ModRQC

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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!)
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.
 

ModRQC

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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.
 

cotedupy

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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.

IMG_3390.jpeg


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

IMG_3387.jpeg


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
 

ModRQC

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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.
 

Desert Rat

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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:

View attachment 120657

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

View attachment 120656

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

cotedupy

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Luftmensch

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For my slate:

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' :(
 

cotedupy

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For my 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' :(
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.
 

cotedupy

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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.
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.
 

Desert Rat

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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.
 

cotedupy

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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.
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 :)
 

cotedupy

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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:
IMG-3543.JPG


Tools for breaking up slate, and tools for making tools for breaking up slate:
IMG-3544.JPG

IMG-3553.JPG


Info regarding the accepted SI units of slate size:
IMG-3556.JPG


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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