Thread: Tsushima "Ocean Blue" 12K

The bevel doesn't always reflect what is happening at the tip-top of the apex/edge very well. That's why it's not wise to judge an edge by micrographs - the shave test is the arbiter. Have a look at a coticule-honed bevel for instance!

There has to be a science behind this we can put our finger on. It's not magic. I understand everyone's beard, skin, hair follicle strength, lather, skin oils etc... is different and that's why you can't say what is good for the goose is good for the gander.

Well, maybe that is the science behind it...

It isn't magic at all. It's just that at the scale of the width of a razors apex, funny things can happen that seem to defy logic. The steel at the apex of a razor is tenths of a micron thick - at that scale it's very flexible, so it tends to push around a bit while honing no matter how light the pressure.

Impacts or pressure from dull grit particles or obtusely shaped particles can do different things to the edge than pointy acute sharp ones - sometimes good things, sometimes bad things. We discover which by honing up a blade and trying it out.

After that the edge could be viewed on something like an FIB scanning electron microscope to see what the cross section of the blade looks like at the extreme apex - this can give some idea of what to shoot for, but the final judge is always the shave. If you haven't already, check out the Science of Sharp blog if you're interested in the subject.

The stone seems interesting.
There is a possibility the stone is indeed a Tsushima; if you dig deep enough, all the pressure from above will compact the stone particles enough, the stone will get hard, and the particles, even if they are same sized, they break up leaving a smoother surface, with less "teeth" on that surface, glazing, and leaving a smoother, more polished edge.
That's exactly what happened with the real Kyoto Jnats, and we ended up with the dull gray asagi stones.
Even as a very fine version that is quarried in Japan, it has nothing to do with the classic favorite ones. The composition is different, it would be more similar to a slate, a Thuringian like maybe, or a hard, mudstone, if it's like the Tsushima I know.
The stamps are really easy to reproduce too, but I would like to think that it's a real deeper Tsushima. I'll try one. Or even better, I'll ask a few friends from Japan if they know about a finer version of the classic Tsushima stone. (Does Tsushima comes from Tsushima? )

I love rocks, so with piqued curiosity I looked at the advert for that stone. Tell me please, would some others who have looked, or perhaps any of those who HAVE one in hand, is the "brand" actually IN the stone? because it looks engraved in to me, not stamped on.

Which would lead me to think this is a manmade stone and not a "mined" stone. And I get a real big kick out of how the "extra large stone is actually smaller but costs 30% more! =P

It's a natural stone.

Originally Posted by Magpie

I love rocks, so with piqued curiosity I looked at the advert for that stone. Tell me please, would some others who have looked, or perhaps any of those who HAVE one in hand, is the "brand" actually IN the stone? because it looks engraved in to me, not stamped on.

Which would lead me to think this is a manmade stone and not a "mined" stone. And I get a real big kick out of how the "extra large stone is actually smaller but costs 30% more! =P

Large stone dimensions: 8.0 x 2.7 x 1.0 Total Volume: 21.6
XLarge stone dimensions: 8.0 x 3.2 x 1.1 Total volume: 28.16

Large stone $4.03 per cubic inch
XLarge stone $4.43 per cubic inch

What have we learned? 1: I have too much time on my hands, and 2 - the XL stone is probably not worth the extra $37.60 for our purposes. 1/2 inch wider on an already nearly 3 inch stone and a smidge thicker will likely not have any effect on honing a razor.

Originally Posted by Marshal

Large stone dimensions: 8.0 x 2.7 x 1.0 Total Volume: 21.6
XLarge stone dimensions: 8.0 x 3.2 x 1.1 Total volume: 28.16

Large stone $4.03 per cubic inch
XLarge stone $4.43 per cubic inch

What have we learned? 1: I have too much time on my hands, and 2 - the XL stone is probably not worth the extra $37.60 for our purposes. 1/2 inch wider on an already nearly 3 inch stone and a smidge thicker will likely not have any effect on honing a razor.

The reason Xl stones carry a premium price per cubic inch is that it is rare to find large pieces of stone that meet the quality requirements. If there is a flaw, they have to be cut down into a smaller stone. Reference the price of Coticules. The price of a large size piece is astronomical because they are so rare.

Originally Posted by Magpie

I love rocks, so with piqued curiosity I looked at the advert for that stone. Tell me please, would some others who have looked, or perhaps any of those who HAVE one in hand, is the "brand" actually IN the stone? because it looks engraved in to me, not stamped on.

Which would lead me to think this is a manmade stone and not a "mined" stone. And I get a real big kick out of how the "extra large stone is actually smaller but costs 30% more! =P

The stamp on the stone is imprinted on the surface of the stone and not etched into the stone. It may be a gold foil stamping.

The stone is definitely natural rock. I calculated the density of the stone as 2.96 g/cc. For comparison, I have a Chinese Guangxi that is 2.89 g/cc. That is probably within the error of my measurements. I do not think you will find any man-made stone that is that dense.

While the Tsushima stone is called ocean blue, I think that is primarily to differentiate it from the ocean black stone. My Guangxi is dark grey with a slight bluish tint while my Tsushima is not quite as dark and has a slight greenish tint. Ocean green would not sound quite as attractive as ocean blue.

Originally Posted by RayClem

The reason Xl stones carry a premium price per cubic inch is that it is rare to find large pieces of stone that meet the quality requirements. If there is a flaw, they have to be cut down into a smaller stone. Reference the price of Coticules. The price of a large size piece is astronomical because they are so rare.

Correct. And there is a reason I settled for a 175 x 50 mm (7 x 2 inches) coticule at $100 rather than springing for a 200 x 75 mm (8 x 3 inches) stone at $275. 7 cubic inches of stone at 14.29 a cubic inch, vs 12 cubic inches of stone at 22.92 a cubic inch. And this without looking at select rectangular stones! They get costly quick!

I understand precisely why a coticule gets more expensive, I've seen how the veins form. I don't know how a Tsushima vein forms, but one can reasonably assume that perhaps it is similarly difficult to find a sizeable chunk of hardened ocean blue stone. But on an 8x3 inch stone with a rolling X stroke half the time my razors don't touch the 1/2" of stone toward the toe of the blade.

Perhaps I should've said for my purposes the XL stone isn't worth the extra 37.60? Paying %42 more for stone I'm not likely to touch with a razor and will only lap down the drain doesn't work in my favor, but if perhaps someone uses it for knives, anything with a wider blade that will touch the extra half inch, or is simply willing to pay the premium for it, then of course it may be worth the money for the wider rock.