Thread: How do you test an unknown natural stone?

This is going to get wordy but some thing to keep in mind when "Testing" unknowns



Your fingers pretty much run out at less then 8k, basically after that the fingers are useless, they just don't have the sensitivity.

The scratch pattern analysis although can be a good exercise can also lead to some very wild guesses.. Don't take my word for this, take three or four 8k synthetic hones and perform a scratch pattern test on each of them, and compare them to each other, you will find that the different types of Grit will give different results so will the difference in binder..
This is where some of the wild grit ratings come from with naturals..
Try using teaspoon bottoms or make actual scratch test squares out of Aluminum rather then using a razor this eliminates the "Honing" variable..
Don't forget the depth of the scratches also, make sure you try and take that into account..

Magnification is fun and we all like pics, but again it doesn't tell us much as to grit, as it can't show us how the grit and binder react together..

One statement I have made over and over about grit ratings:
"Numbers only work within a given series of Hones, therefore I know that a Norton 8k is a higher grit then a Norton 4k, I however do not know that a Norton 8k is higher than a Shapton 6k"..
Numbers may not even hold true for a given brand, take a Naniwa Super Stone 10k and compare it directly to a Naniwa Chosera 10k, these are two different types of cutting grit and two different types of binder and give two different results on the scratch tests and the shave test, yet they are both 10k


Now comes the weird part, your tongue is way more sensitive to the grit differences then the fingers, try licking the CLEAN surfaces, keep in mind this is not accurate either it is just fun, and gives one other indicator. It can however be fooled by the differences in Lapping so be careful with giving this very old test to much credence

What I am basically saying is that it really takes a bit of experience to try putting a grit rating on stones and hones, I honestly try never to Grit rate a natural, I find it inaccurate most of the time, and down right mis-leading some of the time..

Now after all that being said, it should be pretty easy to find a line up for your unknowns by working with your known hones. ie: putting your hones into a working order... Be careful of falling into the "Finishing Trap" where you start stacking stones at the end of the honing progression trying to stretch it out, once you get over the 8k level you don't have much room left to "Finish" so chose your weapons wisely..

To figure out What kind of hone it actually is, ie: Thuringen, Coticule, CF, Arkansas etc: entirerly based on comparison to known stones..

So true because all of these test, are so subjective, any of these test will only give you a ball park of grit range. For me a quick way just to see if it has finishing potential. Visual stria or stone smoothness does not always equal sharpness and or comfort, e.g. The Frictionite.

I find stone prep and honing pressure, to be the most critical factors, especially with novaculites and I suspect, with almost any finisher. High grit finishing Arks has a dramatic effect in edge quality as does slurry grinding on finishers, much the same theory of affecting how grit affect the edge.

In the end it all comes down to the shave, with that razor, buy that honer.

Enter the great equalizer…paste.

Well, if you really want to test an unknown here is what you do: get yourself a big hammer and break up the stone. Then you grind it up to a consistency of talcum powder and then you take it to your local University to the Mineralogy Department and have them run it through an X Ray Diffractor. Then you will get a diagram which can be analyzed and then you will know exactly what you have.

Of course it's up to you to reconstitute the stone to determine how well it hones. That is more problematical.