Thread: Japanese stone hardness testing.

Hello, all!

I was trying to find some sort of time table or reference online for testing hardness of a jnat stone. I know some of you, such as Maxim, use a circular pool of water on the stone and then time how long it takes for the water to dry as a guide for this test. How long would a hard stone allow a puddle of water to sit upon it's surface?

Right now my Nakayama Kiita has had a circular pool of water on the center of it's surface for 35 minutes and hasn't dried at all. I wanted to know if there was a guide or reference.

Thanks!

I don't know of a guide, but since hardness is relative, you could do your own comparisons to other hones you have. You could also do scratch tests in the same way. I know there are tables for scratch tests.

Stone doesn't scratch and DMT 325 credit card plate only makes swarf on the stone.

Water disappearing is more a sign of absorbency (water would sit on rubber, right?) and once you get into a small defined range the scratch test isn't going to tell you much - for example the small MOHS kits with different bits of elements are only useful to define which part of the scale you are on. I would think that an impact test would be the answer, but Rockwell testing units aren't exactly cheap. I think you can get a small set of files by Rockwell that are more exact than the MOHS kits, but I can't remember where I saw them for sale.

Regards,
Neil

My first question would be why is it important to know the hardness since it really doesn't relate to the job the stone is going to do? True the water test just relates to porosity which depends on the particular rock and petrology.

A hardness test only makes sense if you have a few stones to compare.
For one stone there is nothing to test because you have nothing to compare against.
From y experience I think hardness of the stone is related to compactness of grit not how hard it is to raise slurry.
I have hard stones that are extremely tough to raise slurry , but I also have hard stones that are pretty easy to raise slurry.
As far as a approximate test, you can read here:

JNS japanesenaturalstones.com: how to water test

My stone sat for over four hours and no water absorbed into the stone so I dried the stone of myself manually.

Why did I find it important? I was bored so I wanted to play with the stone and experiment.

Originally Posted by mainaman

A hardness test only makes sense if you have a few stones to compare.
For one stone there is nothing to test because you have nothing to compare against.
From y experience I think hardness of the stone is related to compactness of grit not how hard it is to raise slurry.
I have hard stones that are extremely tough to raise slurry , but I also have hard stones that are pretty easy to raise slurry.
As far as a approximate test, you can read here:

JNS japanesenaturalstones.com: how to water test

I'm sorry Stefan, that doesn't make any sense to me. For a honer, the only meaningful definition of hardness is how easily it raises slurry.

If you try honing a razor with water only and the water quickly starts to show slurry darkening, then it's a soft stone. If it shows only very little slurry release, it's hard. What else does hard actually mean in this context?

The water test is one of many methods used by hone dealers to rate the hardness. Some others include pitch (when hit, the higher the pitch of the stone, the harder it is), relative mass and visible porosity. You'll notice, all of these are related to density--there appears to be some degree of direct correlation between stone density and hardness.

The final test of hardness, though, is slurry-raising, because it's the only one that directly effects honing.

Originally Posted by JimR

I'm sorry Stefan, that doesn't make any sense to me. For a honer, the only meaningful definition of hardness is how easily it raises slurry.

If you try honing a razor with water only and the water quickly starts to show slurry darkening, then it's a soft stone. If it shows only very little slurry release, it's hard. What else does hard actually mean in this context?

.

For me hard means it does not absorb much water, also should not auto slurry. The auto slurry IMHO should not be any indicator because there are many medium hard stones that do not auto slurry but are not good for razor finishing.
The two stones I referred to are very hard according to the water test, one is easy to make slurry with a diamond plate the other one is very hard to, and neither auto slurries.

Originally Posted by Disburden

Hello, all!

I was trying to find some sort of time table or reference online for testing hardness of a jnat stone. I know some of you, such as Maxim, use a circular pool of water on the stone and then time how long it takes for the water to dry as a guide for this test. How long would a hard stone allow a puddle of water to sit upon it's surface?

Right now my Nakayama Kiita has had a circular pool of water on the center of it's surface for 35 minutes and hasn't dried at all. I wanted to know if there was a guide or reference.

Thanks!

Since evaporation is a big part of this and humidity varies
so widely you are not likely to find any table.

Now, If you had a quarry and lined up fifty
hones you cut today this is a different thing.

Dip a hone in a bucket and set it out...
one after another all fifty --- and watch
to see if they are the same or not. If there
is a lot of difference sort them with this
water test and then check the groups to
see how they build a slurry and hone steel.

You would also look to see if the rock sucked up
water in odd and uneven ways. A hone should
be even across it's full surface if it is to wear
and hone evenly.

In the end there is only one test.. "The shave test."