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Can you use slate for polishing?


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Hi Everyone,

 

I had some left over slate from the lot that I had installed in my basement floor. The slate is from India and was quite soft and made a nice smooth slurry when cutting. That got me to wondering about its potential use as a waterstone. So far I have used a piece as a waterstone for sharpening knives and I polished an axe head. It works wonderful, producing a fine smooth slurry, and gets the blade shaving sharp. The axe head polished up nicely without scratches.

 

Now I am wondering if it would be useful as a polishing stone (s). Some of the slate seems to produce finer slurries, depending on the colour. Of course, the grit would have to be uniform, so no scratches would form. If it works, at $2.50 a square foot, it would beat Japanese water stone prices.

 

What do you think? Has anyone tried it? I will have to experiment with the stuff I have.

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So far I have used a piece as a waterstone for sharpening knives and I polished an axe head. It works wonderful, producing a fine smooth slurry, and gets the blade shaving sharp. The axe head polished up nicely without scratches.

 

Haven't you sort of answered your own question? :)

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Haven't you sort of answered your own question? :)

 

Possibly! But the axe head was a rusty old one, not a newly forged blade. Also, I wonder if it would create a similar finish to a proper water stone, polishing away the softer steel crystals. I will have to experiment further. I was just wondering if anyone else has tried it out or even contemplated it? I don't want to set myself up for failure, if this has already been done unsuccessfully.

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Aarne,

 

I HAVE tried slate for polishing. I also have a small lot of it, big enough to do a kitchen. I thought the slurry would be useful. So I put it through its paces on various blades in various states of polish. My conclusion is that it would NOT work past the binsuido stage, due to the inclusion of some rather large, sandy particles. As a matter of fact, it was so sandy and scratchy, I decided it was not useful at all because the scratch pattern was just too random and difficult to remove with kaiseido.

 

As you stated, it is very soft. Of course, the very sandy inclusions could be in just the lot I have. Natural Japanese stones vary a lot, as well. Stones next to each other can vary in use and expense by even several hundred dollars.

 

I came to the conclusion many years ago that, for me at least, I need a very hard, durable binsuido for most of the monosteel work. Otherwise you deform the blade because the stone becomes deformed very quickly--or I spend entirely too much time reshaping the stone. So, it is not worth my time reshaping so much just to utilize this material.

 

I guess, if you had a need for a stone that only went up to 325 g and was very soft and formed a slurry, you could substitute slate. But you definitely cannot efficiently shape the blade with it, so I couldn't justify any usefulness. And usually you hone / sharpen at higher grits where the slurry is useful. The slurry off binsuido and kaiseido is just rinsed away--it rather hinders efficient shaping and scratch removal.

 

I think you found the best use for it, polishing-wise: large, possibly rusty tools that don't have a really acute edge and don't matter if they are "scratchy" looking.

 

BTW, tried it first as hazuya on hamon of a blade in finish polish--RE-learned why you check hazuya on a blade in kaiseido before using it, later. Jeesh, it really made a mess....

 

This is just my opinion, of course. I hope it was helpful. I am sure there is slate out there that would make a wonderful kaiseido, or even nagura. MAYBE even uchigumori, as I believe the two stones are formed similarly in a geological sense. However, I have yet to find any that would work that way. I can just imagine asking slate companies for samples from various lots to test this way. I wish I had the time....

 

Sincerely,

 

Shannon

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