Thread: What actually is Hardness in natural stones, and how it affects sharpening

I've been following this thread but have had a bit of difficulty understanding the latest developments, so please put me in line if I'm wrong here.

A stone's 'hardness' can be determined by how quickly it releases its own particles. A 'softer' stone releases its own particles more quickly than a 'harder' stone of the same type (i.e. Coticule.) A 'softer' stone must therefore be 'faster' than a 'harder' stone of the same type, because more of its own particles are released during honing, which facilitates the removal of more steel. This works fine when comparing two of the same kind of stone (apples to apples) but doesn't seem to work when comparing two different kinds of stones since the 'hardness' of a given stone is relative only to that particular family of stones.

If there's no standard for measuring hardness in a stone, is there a standard for measuring a stone's grit rating? Regardless of whether a stone is hard or soft, fast or slow, coticule or j-nat, isn't the 'equivalent grit' really the most important characteristic of the stone, the one that defines it's intended use and function?

The scientific explanation of the "grit" is not the most important characteristic of a stone. I don't think there is one "most important characteristic of a stone" that makes it a good hone. It's the overall image of a stone that makes it a good or fast or fine hone. It wouldn't be really useful even if a standard measuring method of a natural's hone grit existed. There are many variables, and its grit is just one of them. Not the most important, and certainly not the least. An example are the coticules. The grit we re giving them regarding their performance is 10k to 15k in some cases. Their actual grit is 1000 to 4000 grit (5 to 15micron). The shape of their abrasive garnets is what makes them perform like a very fine hone.

After that, its the lubricant someone uses.
A yellow lake with water has a grit around 8 to 10k. The same stone with oil has a grit around 12k.
This sentence does not makes sense.
The size of the abrasive particles remain the same. It's their abrasive abilities that the lubricant chances. With water they cut deeper than with oil.
There are no rules with the naturals, even with the man made hones. If you have some experience, try it, and you will find out if you like its characteristics or not.
It's not hardness, it's not grit, it's not the color, it's not the name (Charnley, thuringian, coticule, nakayama etc). It's what you like when you hone your razor, and how it feels when you shave with it. I know my answer is not helpful, but, that's how I think it is.

Originally Posted by Vasilis

The scientific explanation of the "grit" is not the most important characteristic of a stone. I don't think there is one "most important characteristic of a stone" that makes it a good hone. It's the overall image of a stone that makes it a good or fast or fine hone. It wouldn't be really useful even if a standard measuring method of a natural's hone grit existed. There are many variables, and its grit is just one of them. Not the most important, and certainly not the least. An example are the coticules. The grit we re giving them regarding their performance is 10k to 15k in some cases. Their actual grit is 1000 to 4000 grit (5 to 15micron). The shape of their abrasive garnets is what makes them perform like a very fine hone.

After that, its the lubricant someone uses.
A yellow lake with water has a grit around 8 to 10k. The same stone with oil has a grit around 12k.
This sentence does not makes sense.
The size of the abrasive particles remain the same. It's their abrasive abilities that the lubricant chances. With water they cut deeper than with oil.
There are no rules with the naturals, even with the man made hones. If you have some experience, try it, and you will find out if you like its characteristics or not.
It's not hardness, it's not grit, it's not the color, it's not the name (Charnley, thuringian, coticule, nakayama etc). It's what you like when you hone your razor, and how it feels when you shave with it. I know my answer is not helpful, but, that's how I think it is.

It makes sense in a way, I think. I don't have any real honing experience yet, I had hoped that there was a simpler way of classifying natural stones but it would seem that I'll have to personally experience them before I can really wrap my head around them. Is there no other way to determine what kind of edge a particular stone will give without actually honing on that particular stone?

Originally Posted by Pato

It makes sense in a way, I think. I don't have any real honing experience yet, I had hoped that there was a simpler way of classifying natural stones but it would seem that I'll have to personally experience them before I can really wrap my head around them. Is there no other way to determine what kind of edge a particular stone will give without actually honing on that particular stone?

Regarding most naturals, each stone is unique, even between hones of the same kind. After that, here on the forum we have a way of comparing the finishing qualities of natural hones with the man made ones, and this way we say for example "escher hones are around 12k" (we don't know its grit, it's just the finish on the edges that makes us think it's 12k, and the feeling on our faces while shaving). Usually, again, we re referring to grit. But there are hundreds of other parameters that combined, make a hone worth of praise. Check out this page. Hones - comparison table - Straight Razor Place Wiki It should help you.
But in the end, if you wont try one for yourself, you can't say if it will be good or not. When I started, I only used slate hones. After having some experience with them, I tried some oilstones. I hated the feeling, and the edges weren't as fine as they supposed to be. It took me months of honing for getting used to them, and achieving the finest edges. Try to find any SRP members of woodworkers or old people ( :P ) near you and ask them to show you how to hone, and check their stones yourself. Even if you have to pay them, you will save money from ordering cheap stones from eBay.

Originally Posted by Vasilis

Regarding most naturals, each stone is unique, even between hones of the same kind. .

While I agree with you, to help Pato out, there are a few shortcuts and that is by going by certain brand names, particularly of the old stones. With arkansas stones, it is easier because even though each stone can be slightly different, the grading of the best manufacturers of Pike and Norton was so consistent that you could be pretty sure of the quality of stone you were getting just by their label on the stone and on the box. If you got a surprise, it was usually a good one meaning that the stone was actually better than its label and somehow slipped through the grading process. I know of no other arkansas stone companies that were as consistent in their grading or offered as high quality a product.

I won't say anything about Eschers and such as I don't have enough experience with them, but coticules, while all over the place as far as quality goes, had some companies selling them that seemed to have a very consistent grading system as well. A couple of these were Old Rock and Choice Razor Hones, although I have had some Old Rock coticules that were excellent and some that were nothing special. Rumor has it that these were some of the later hones from them. Can't say for sure on that. Choice Razor Hones have always been consistently some of the best coticules sold with a label. The Pike coticule I have is also one of the best, but there are such few around no can can get a large enough sample of them to be definitive. Pike has always been consistently good in their grading of all their high end stones in my experience though and I have compared over 50 of them.

Others can probably vouch for some other consistently good brands, but most won't do so because they are always on the search for the good ones and the more people that know about them, the less available they are. And who can blame them - same with fine quality straight razor brands. Best advice is, once you find a brand that you like, look for more of them and see for yourself how consistent the brand is.