# slate as a sharpening stone



## lurcher (8 Apr 2015)

hi does anyone use natural slate for tool sharpening ? .
i was playing out today and was playing detective i bought a welsh slate stone along time ago and lost it in the depths of my workshop / playroom today i found it again so out came the old norton dusted it off and oild her up set to with an old chisel that has had some grief of late .
iforgot how good the the old norton stones are so put some oil on the welsh slate and it worked very well with the final pollish and alot cheaper than jap stones give it go you may like it,


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## lurker (8 Apr 2015)

I wish my shed was big enough to have hidden depths :lol: 

I have a chunk of honister gap slate I want to try for the same purpose


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## MIGNAL (8 Apr 2015)

I have a Slate stone somewhere. . . I think I had a very quick try with it about 2 years ago. It seemed to be a very fine cutting stone. Not as fast as my 8,000 G Japanese waterstone but it seemed a bit faster than my fine Arkansas - which is slow. I'm pretty sure that I tried it with water rather than with Oil. I'll see if I can dig it out (cough) and give it another trial.


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## dp341 (8 Apr 2015)

I've got my Dad's old charnley stone from Charnwood (where he was born and brought up), a massive great chunk in a box he made long before I was a twinkle in anyone's eye. I wouldn't want to be stuck with it as my only sharpening stone but for a finish polish it's great.


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## lurker (8 Apr 2015)

dp341":26e78qo7 said:


> I've got my Dad's old charnley stone from Charnwood (where he was born and brought up), a massive great chunk in a box he made long before I was a twinkle in anyone's eye. I wouldn't want to be stuck with it as my only sharpening stone but for a finish polish it's great.



If you nip down the m1 sometime I can take you to see the quarry where the best stone reputedly was found.


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## adrspach (8 Apr 2015)

If you use usual slates with water they are faster but not as fine as they will be with oil. Big advantage of slate is cheap and you can get it in much bigger sizes and shape it as you need.
The Honister slate would be interesting to try. I was there few times but so far had a no intention as it is not known for hone use.
CF is not slate it is novaculite which can be significantly slower but finer. I am not sure how much it would be effective for a woodworker to use it nowadays with moderns waterstones and diamond plates like available.


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## woodbrains (9 Apr 2015)

Hello,

Up until about 10 years ago, my main sharpening stones were a set of oilstones and I used a Welsh slate as the last step just before a leather strop. For less demanding work I omitted the strop. They are very. good in fact and a little quicker than black Arkansas. They do hollow out quicker, but can be flattened in no time with cloth backed abrasives or whatever. I was happy with the performance and still use them from time to time. I changed to water stones though, which are quicker, especially on modern steels such as A2 and negate stropping. (At 8000g) If I was only able to use my oilstones again, I would still be happy, but I find water stones so much more convenient now. TBH cost is the least consideration and I still think water stones can be bought, not significantly more expensive than any other sharpening media, _for the same level of sharpness._ slate is probably around the same effectiveness as 3000-4000 water stones and these are not expensive and much faster. 

Mike.


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## Cheshirechappie (9 Apr 2015)

Another here impressed with a slate polishing stone - mine's a Dragon's Tongue bought from Inigo Jones. I use it with oil, and just finish the edge of a chisel or plane-iron previously re-honed on a fine India by drawing the edge back along the slate stone about five or six times holding it at a very slightly higher angle than on the India, then alternating bevel and flat side - again just drawing back along the stone - four or five times to work off any burr (I don't deburr on the India if subsequently polishing on the slate). That gives me the best edges I've ever managed, even including the waterstones I used to use years ago. Another plus is that I can use the slate stone at the bench - no water slopping around!

The slate doesn't really cut much at all, but it does seem to burnish or polish edges very well. It's not so good on polishing plane-iron flat faces - it just takes too long to get any sort of positive result, though it would probably work using the ruler trick.

Just in passing, I'm not sure that the 'proper' slate hones are technically slate at all - mine has no discernable cleavage planes. I gather they are made from a material properly called 'hornfels' which is often found in the same areas as slate beds, but is geologically slightly different. In slate, the mineral grains are aligned by pressure to give the characteristic easy cleaving into thin sheets, whereas in hornfels the mineral grains are not so aligned.

Whatever the technicalities, they do make a very good finishing stone.


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## bugbear (9 Apr 2015)

Cheshirechappie":1r8lkgzx said:


> Another here impressed with a slate polishing stone - mine's a Dragon's Tongue bought from Inigo Jones. I use it with oil, and just finish the edge of a chisel or plane-iron previously re-honed on a fine India by drawing the edge back along the slate stone about five or six times holding it at a very slightly higher angle than on the India, then alternating bevel and flat side - again just drawing back along the stone - four or five times to work off any burr (I don't deburr on the India if subsequently polishing on the slate). That gives me the best edges I've ever managed, even including the waterstones I used to use years ago. Another plus is that I can use the slate stone at the bench - no water slopping around!
> 
> The slate doesn't really cut much at all, but it does seem to burnish or polish edges very well. It's not so good on polishing plane-iron flat faces - it just takes too long to get any sort of positive result, though it would probably work using the ruler trick.
> 
> ...



Well, the details DO matter - slate is a huge category of stones, and some are (much) better than others.

Inigo Jones spent some (lots!) time finding slate which is good for honing. The details
of particle size, particle uniformity, particle shape, sharpness and bond strength all matter.

BugBear


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## adrspach (9 Apr 2015)

There are many types of slates as already said. 
During my time which I spent in Inigo Jones I was shown how Dragons Tongue can be split with cleavage lines.
The finishing quality of slates can vary. Some of them are not usefull for anything than builders infill as they have huge ammount of inclusions. On the other side there are some which can be used for finest finishing on straight razors and such fine tools. Even DT particle size can vary. This is normal for natural stones. So far in stones which went through my hands the estimates were between equivalent of japanese waterstone 3000-10000 grit.
Most of them do gouge easily but also can be reflattenend quickly on flattening plate.
Slate is very cheap comparing with modern waterstones ( I believe I. Jones sells DT 8x2" for about £10). There are other slates available on the market some of which are sold under fake names and labels.
I do have quite few slate hones and slipstones in my collection of different sizes and use them every so often when time and mood is right. At the end it is for fun.


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## MIGNAL (9 Apr 2015)

Anyone ideas on this:





This is the stone that I assumed was slate. It came in with a lot of other old tools that were given to me. It's obviously double sided. The lighter coloured side cuts very slowly, seems fairly hard, the blade just seems to skate along it. The darker coloured side cuts reasonably well, creating a bit of a slurry and seems soft(ish). I used water. Not as fast as my 8,000G Waterstone but it's pretty good. Strop after and the blade seems as sharp as the waterstone + strop. 
It's a small size. 2" x 6", so it may have been sold more for razors or knives.


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## bugbear (9 Apr 2015)

MIGNAL":1d0m3l5o said:


> Anyone ideas on this:
> 
> 
> 
> ...



Is the boundary between the two layers straight or wavy?

(and do you have a larger, better lit photo?)

BugBear


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## MIGNAL (9 Apr 2015)

It's straight, you might say ruler straight.
Actually the lighter coloured side has a very slight Greenish tinge to it, a little mottled with darker spots, at least on the edge. The darker side has a few very light grooves, which probably indicates that it is towards the softer side of things.
I have given the size wrong, it's 1 1/2" x 6".


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## bugbear (9 Apr 2015)

MIGNAL":36xwb21d said:


> It's straight, you might say ruler straight.
> Actually the lighter coloured side has a very slight Greenish tinge to it, a little mottled with darker spots, at least on the edge. The darker side has a few very light grooves, which probably indicates that it is towards the softer side of things.
> I have given the size wrong, it's 1 1/2" x 6".



OK, that eliminates my main candidate, which was Belgian/Ardennes Coticule.  

BugBear


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## Sheffield Tony (9 Apr 2015)

Secret Santa brought me a slate stone of some kind a couple of years ago. I use it a fair bit. In fact I find myself using a double sided Norton stone, and then if it matters (e.g, carving) the slate stone. It is not as good in most respects - (slower, easier to damage) as the small hard Arkansas stone I have - but it is bigger and usually to hand !

It was very easy to recondition though; washing off the gunk with paraffin then Wet or dry paper to flatten it off.


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## adrspach (9 Apr 2015)

MIGNAL":1louseyh said:


> Anyone ideas on this:
> 
> 
> 
> ...




Can you show pictures of bot faces preferably wet?
I have one favourite which is in fact two homegrown stones in one.


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## MIGNAL (9 Apr 2015)

OK. Improved photo's. The first one clearly shows the Greenish slightly mottled appearance, with some striation? or inclusion? Whatever they are termed. 






The darker coloured side. Much more homogeneous looking. Pretty sure it's still natural. It's just a very dark grey Slate colour! It's this side that interests me, largely because I find the faster cut to be much more useful that the other side.


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## adrspach (10 Apr 2015)

What you have there is so called Scotch hone. One side is Tam O shanter and the other is very highly likely Water of Ayr.
Very nice combo hone which is invaluable on some steels more prone to tearout on the edge.


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## MIGNAL (10 Apr 2015)

Thank you Adrspach. Good to put a name to it. 
I've just done a quick experiment with this stone. I put a secondary bevel on a blade using this stone, the primary bevel was from my coarsest stone that I have - which is an Oil stone. I guess that the Oil stone is at near 320 G, it leaves a similar scratch pattern to my Diamond at 320G. Fairly coarse. This coarse primary bevel was taken right to the edge (and over) the tip of the blade. I wanted to see how long it took this Scotch stone to remove the deep scratches. Not very long, 7 or 8 forward/backward strokes. Probably a few more than my 8,000 Japanese waterstone. I don't know what the grit size is but it does work up a bit of a slurry. In fact it gives a similar 'feel' to the fine Japanese stones. I would be very shocked if it's near some of the sizes quoted for some slate stones i.e. 8,000, 10,000+. My very rough guess would put it at 4 or 5,000. I only used the dark side of this stone. I guess that's the Ayr bit, which is supposedly finer in grit than the other side!
After stropping it cut hairs easily. I tried the blade on some Bubinga and it seemed no different to my Japanese waterstone + stropping, which is about as sharp as anything needs to be. I need to live with it longer but it may well be a decent substitute for the usual polishing stones.


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## adrspach (10 Apr 2015)

A lot of people use strops with pastes which then in effect levels all the differences between hones.


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## CStanford (10 Apr 2015)

adrspach":2yrlh6g0 said:


> A lot of people use strops with pastes which then in effect levels all the differences between hones.



Very true.


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## MIGNAL (10 Apr 2015)

Well I guess it can be said that stropping and paste is fantastically cheap compared to a 10,000G stone. I bought a bar of the Green stuff 10 years ago and I doubt that I've gone through 1/50 th of it!


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## bridger (10 Apr 2015)

once long ago I had a slate/sandstone two sided stone from china. it was too slow to be useful to me.

a couple of years ago I bought some slate tiles at the local builder's supply and cut them up to hone sizes and flattened them. they were spectacularly unsatisfactory as sharpening stones. so soft that the surface quickly became rutted, so slow cutting that I'd die of boredom before getting to an edge and the effective grit was much lower than the look or feel of the stone would indicate (it scratched the heck out of the tool).


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## Cheshirechappie (10 Apr 2015)

bridger":3ea4qrs9 said:


> once long ago I had a slate/sandstone two sided stone from china. it was too slow to be useful to me.
> 
> a couple of years ago I bought some slate tiles at the local builder's supply and cut them up to hone sizes and flattened them. they were spectacularly unsatisfactory as sharpening stones. so soft that the surface quickly became rutted, so slow cutting that I'd die of boredom before getting to an edge and the effective grit was much lower than the look or feel of the stone would indicate (it scratched the heck out of the tool).



As Bugbear pointed out earlier in the thread, 'slate' is a word that covers a great variety of rocks. North Wales, for example, has many slate deposits - there's barely a hillside that hasn't been scratched at for slate at some time or another, and some of them very extensively - but there are very few deposits that make decent honing stones. To take any old roofing slate or slate slab and assume it will match the commercial hones is very likely to give unsatisfactory results. Might still make a very passable roof, though.


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## bridger (10 Apr 2015)

the stuff was cheap enough to give it a try.

no idea where the material was quarried.


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## adrspach (10 Apr 2015)

My guess if ti was new at that time Brasil, Portugal or China were main imports here.


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## sdjp (13 Apr 2015)

Cheshirechappie":1o3ff0jn said:


> The slate doesn't really cut much at all, but it does seem to burnish or polish edges very well.



Indeed - I have a similar welsh Dragons Tounge, and it's perfect for the straight razor - not least because it polishes well, without cutting too much. I've yet to take the chisels to it, but great on knives after a 3000 grit ceramic. And huge - 9x3 inches … no need to faff to get the blade covered.



Cheshirechappie":1o3ff0jn said:


> Just in passing, I'm not sure that the 'proper' slate hones are technically slate at all - mine has no discernable cleavage planes. I gather they are made from a material properly called 'hornfels' which is often found in the same areas as slate beds, but is geologically slightly different. In slate, the mineral grains are aligned by pressure to give the characteristic easy cleaving into thin sheets, whereas in hornfels the mineral grains are not so aligned.



Ah, that makes sense!

Both slate and hornfels are metamorphic rocks - converted from others by heat and pressure. Hornfels tend to be heated more in the transformation, which fuses the layers, and leads to a typically cubic fracture plane; whereas the slates are under more pressure, hence the differing transformation. Also, slate can be transformed into hornfels, by subsequent processes, but I'm not aware of any cases of hornfels -> slate transformations.


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