Thread: Natural Japanese waterstones

Ah... I get it. Hadn't factored in heat that way: was thinking only of sedimentation and compression... forgot about Japan's formidable and volatile geography.

Thanks for making that so perfectly clear.

Becky

p.s. No, Steve, they're not unappetizing (though quite foul)... that's just jealousy on my part. But I'll deny ever having said it.

b

Originally Posted by Sheets

My feeling, Neil, is like what Russel said about etching steel. If there is an acidic element to the slurry (because the breakdown and exposure of the stone into its grit + bonding material. Water can and does produce acid when mixed with certain kinds of rock - sometimes a big problem in the mining industry. And we all know what scotch on the rocks can do). Now, obviously this would be on a very mild scale, but when we are talking about the size of the scratch pattern with grit in the micron size, even a slight action would (I believe) have an effect.

...snip...

Hey Russel, I'm interested in your litmus test (I thought of that, but don't have any litmus paper and I ate all my red cabbage a while back). So, please do if you can (we might as well be thorough).

Steve - You could be right about an acidic effect. As original sediments can be either acid or alkali, and given that metamorphic process doesn't destroy the chemical composition of resulting stone, an acid slurry is a possibility.

Like you, I will be interested to see if Russel can take a pH breading and let us know the results.

Neil

I may beat Russel to it. I got a red cabbage, so can (and did) make some home-made litmus paper. Haven't got to the acid test yet, though. But I'm starting to feel like I'm barking up the wrong tree.
One would have thought that after all these years, the Japanese would have figured it out and built a tradition based on this effect. But will see what the science says anyway.

Steve

I'll be interested in seeing if there is any significant pH change, but I'll be pretty surprised if there is. Acid is used to re-etch files and rasps, so it is clear that acid can help sharpen an edge on a tool. But the process for this is fairly lengthy, on the order of 12-24 hours.

Given the relatively short exposure time of the tool to the water on the waterstone, it would have to be a pretty strong acid to make an impact on the metal of the tool being sharpened, and I don't think that hydrochloric acid, or some similarly strong acid, is released as a waterstone gets wet.

None, nada, nil, zilch. I couldn't detect any ph change on any of my natural stones (not really surprised). I did test my paper before hand to make sure it would show a colour change in the presence of acid (lime juice, grape juice and vinegar). So I think its safe to list list theory as BUSTED
Any other bright ideas out there?

Steve

Originally Posted by Sheets

None, nada, nil, zilch. I couldn't detect any ph change ...snip....So I think its safe to list list theory as BUSTED
Any other bright ideas out there?

Steve - am I right in thinking that what you are trying to understand is why natural stones are better at highlighting the difference between the soft iron (jigane) and hard steel (higane), or am I off on a tangent on this one? The original question has become a little blurred for me going back in the origins of this thread.

According to one expert (Alex), there is not an obvious scientific explanation:

"The scratch marks left by the man-made synthetic stones look deep and long when compared to the scratches left by the natural stones. This is typical of synthetic stones which are formulated to cut aggressively and fast. The hard cutting compounds, usually a proprietary ceramic or oxide of some form, do not break down into smaller particles as readily as the organic compounds do in the natural stones. The synthetic stones tend to leave the soft iron or jigane looking scarred under magnification, but when viewed with the naked eye the hagane and jigane look equally shiny. I do not have a scientific explanation for this phenomenon. Natural awase toishi tend to leave the finished blade with more contrast between the hard steel and the soft iron." http://thejapanblade.com/


Alex also provides a very helpful explanation of the sharpening process in relation to man-made, natural and nagura stones. The site is a bit confusing in its navigation, so here is the direct link: http://thejapanblade.com/nagura_use.htm


Neil

Hi Neil,

I've seen Alex's site (makes me weep to see those stones he has).

The original question someone asked was why natural finishing stones seem to be able to impart such a markedly superior edge (sharper and stay sharp longer) on Japanese tools as compared to man made stones. Finer grit was one aspect, but the feeling people have that there is something else beyond that, was what we were trying to investigate.
The fact that the ha and ji are so well differentiated is another point of mystery, but not part of the original question as I recall. My feeling (guess) on this is that the natural stone has a larger range of particle (size still all very fine) and this makes the softer steel less reflective (the scratch pattern is less uniform, so light reflects differently than a more constant surface).

Steve

Originally Posted by Sheets

The original question someone asked was why natural finishing stones seem to be able to impart such a markedly superior edge (sharper and stay sharp longer) on Japanese tools as compared to man made stones. Finer grit was one aspect, but the feeling people have that there is something else beyond that, was what we were trying to investigate.
The fact that the ha and ji are so well differentiated is another point of mystery, but not part of the original question as I recall. My feeling (guess) on this is that the natural stone has a larger range of particle (size still all very fine) and this makes the softer steel less reflective (the scratch pattern is less uniform, so light reflects differently than a more constant surface).

OK, Steve, I'm back on the same page.

I think you have as good an explanation as I can come up for the differentiation in Ji/Ha appearance.

On the sharper for longer question, unless a new theory/evidence comes to light, the explanation I lean towards is the variation in fine grit sizes that develops as the natural stone is worked. The mix of grit sizes creates a micro-serrated edge that exposes fresh sharp cutting 'peaks' as adjacent 'peaks' wear/break away. Although not visible with the naked eye, this micro-serration effect is readily felt when slicing with a hand-forged Japanese kitchen knife that has been sharpened on a natural stone (rather than a man-made stone). For example, ripe tomatoes can be sliced paper thin - i.e. if you ever wanted to do that and the edges do stay sharp for ages, well until some uncouth person starts chopping instead of slicing food with them .

Neil

Originally Posted by NeilS

..... I purchased a Nakayama white karasu finishing waterstone, another hard stone, with medium abrasion and a super-fine grit (approx #20,000), with a few (toxic) lines/spots with coarser grit that has to be removed to avoid scratches on the polished surface.

The Nakayama is a good stone in the hands of a highly skilled (and knowledgeable) user, but it was still beyond my skill levels at that stage of my development. I may have given Nakaoka-san an incorrect understanding of my skill level! So it was back to the man-made stones.

Then a new Japanese woodworking tool and stone seller appeared on eBay, and he (Soatoz) was also located in Australia. After some email exchanges with Soatoz, he offered to assess my Nakayama stone. The verdict was (having examined my efforts on the stone) I needed a softer stone to develop my level of expertise. He recommended a few stones, including a Takao. This is a light yellow finishing waterstone - a softer stone, with medium abrasion power and fine grit (approx #16,000). This new stone, along with a new diamond plate for flattening stones and raising a slurry, got me finally going and experiencing what the natural waterstone thing is all about.

Visited this thread again after just posting to the thread by Thumbsucker on waterstone hardness, and thought I should do a brief update.

After using the Takao regularly for some time I went back to my Nakayam to suddenly find that it had improved no end. Not sure how it did that just sitting there in its box doing nothing for so long...

Anyway, its now my go to stone for the final polish and I like it a lot. And to think I almost gave up on it and even considered selling it at one stage.

The Takao has now been repatriated to the kitchen where it does an excellent job on the my hard (blue) steel edge Japanese knives.

So, if you end up with a natural stone that doesn't work for you immediately, put it away for a while and it might magically improve while you are ignoring it...

.....