What kind of stone is this?

[GLFaria]

Hi

Some time ago this chunk of a stone, about 80 x 40 x 20mm, came into my possession in a very sorry state.
It had been used for sharpening or polishing some implement, I can't guess what (neither wood nor metal were manufactured where it came from).

It is a very soft grey stone wich, when I somewhat dressed it with 180 grit wet/dry with water on a plate glass, made a very fine greyish slurry. It seems to stand water well, and dries quickly.

The finish I get with it in steel is properly mirror-like, quite better than the finish I get with the finest polishing paper I have, which is 4/0 (which was already good enough for the final polishing of metalography steel samples, for which I often used it). So, as long as it lasts, I have come to giving the final touch on the edge of my cutting tools with this stone.

Is it possible to tell, by the sight of it, what kind of stone is this?
Should it be used with water, oil, or dry? (I use it with water, or even dry, but one never knows...)

Thanks for any possible enlightenment

G.

 

[rafezetter]

I'm guessing a bit here but that looks very much like Pumice, (from volcanic eruptions). You may be familiar that Pumice powder is used in french polishing and also as a grain filler.

I would use water / window cleaner personally as a lubricant, although dry would work too, as the voids are so large they could be prone to clogging and would need rinsing out.

 

[bugbear]

Pumice powder is widely used a mild abrasive - but I've never heard of pumice pieces being used.

BTW, what's 4/0 paper on a more standard (CAMI/FEPA/micron) measure?

BugBear

 

[Jacob]

... but I've never heard of pumice pieces being used.

....

A piece of pumice used to be common in every kitchen for various polishing and mild abrasive uses. Often mouse shaped making it handy to grip, with a flat underside. I would have thought too soft for sharpening but no doubt there are grades etc.

 

[KevM]

I would have thought too soft for sharpening but no doubt there are grades etc.

As you say there certainly are different grades and densities of pumice, there's also Scoria which appears superficially similar to pumice but has a higher iron and magnesium content replacing some of the silica. Scoria tends to be denser, harder and darker with bigger bubbles.

They're both igneous volcanic foams that have de-pressurised, off-gassed and cooled so quickly that the champagne spume is frozen. So what you end up with is a very low density igneous glass foam, which although mechanically weak will produce very fine particles of friable glass when ground, hence its ability to polish steel, glass etc. You can buy crushed pumice as pumicite for finer polishing applications.

Here's a nice article on pumice.

 

[bugbear]

This page looks helpful;

http://www.reade.com/Products/Minerals_ ... umice.html

Quite coarse, but with a very low Moh rating. If it breaks down in use,
they actual particle size could be pretty much anything.

BugBear

 

[monkeybiter]

A piece of pumice used to be common in every kitchen for various polishing and mild abrasive uses. Often mouse shaped making it handy to grip, with a flat underside. I would have thought too soft for sharpening but no doubt there are grades etc.

I thought they were a bathroom item for rough skin on the feet.

 

[RogerBoyle]

A piece of pumice used to be common in every kitchen for various polishing and mild abrasive uses. Often mouse shaped making it handy to grip, with a flat underside. I would have thought too soft for sharpening but no doubt there are grades etc.

I thought they were a bathroom item for rough skin on the feet.

LOL +1

 

[adrspach]

Can you disclose any more about the stone history? How does it smell when wet? Does it get blackened quickly with swarf? Does it slurries easily? Any pictures of slurry? If you can try can you put a drop of vineagar on it and check (best with some magniffication) if it makes bubbles? Any cracks or original chips in it? If yes can you show picture of them?
I know many questions but all of those can change the result. At present I am between manmade hone and Travertine.

 

[Fat ferret]

Does it smell of feet? :lol:

 

[adrspach]

Would you be surpried if I tell you that i have met people who are able to hone with their feet and do it well?

 

[bugbear]

Would you be surpried if I tell you that i have met people who are able to hone with their feet and do it well?

Are we talking Christy Brown here, or an unusual abrasive?

BugBear

 

[Owl]

When I was serving my apprenticeship ( 1948/ 1954 ) pumice stone was commonly used for rubbing paintwork down prior to repainting, this included not only woodwork but also painted walls.

 

[adrspach]

Would you be surpried if I tell you that i have met people who are able to hone with their feet and do it well?

Are we talking Christy Brown here, or an unusual abrasive?

BugBear

In late 60th 70th there wa drog used for morning sickness I think called Chalidomide which left a lot of babies disfigured. Those who i met were able to write, wash their hair and simillar jobs with their feet. Not all of them are famous. they just wanted to live and enjoy their lives.

 

[sdjp]

BTW, what's 4/0 paper on a more standard (CAMI/FEPA/micron) measure?

4/0 sounds like it's 4/0 _emery_ paper. Looking that up, http://www.cafa-info.org/grit.html says P1200; I'd had it in my memory at P2000, however, and can find informal support for that. Somewhere in that band for sure.

 

[bugbear]

Would you be surpried if I tell you that i have met people who are able to hone with their feet and do it well?

Are we talking Christy Brown here, or an unusual abrasive?

BugBear

In late 60th 70th there wa drog used for morning sickness I think called Chalidomide which left a lot of babies disfigured. Those who i met were able to write, wash their hair and simillar jobs with their feet. Not all of them are famous. they just wanted to live and enjoy their lives.

I didn't know whether the reference was analogous to the stropping ON the hand, mentioned recently, only ON the feet instead, hence my question.

BugBear

 

[GLFaria]

Hi

I must thanks everybody who has been helping. It has been impossible for me to reply in the last couple days.

There is a number of questions I must answer, I can't do it right now, I will try to reply later today.

G.

 

[GLFaria]

BTW, what's 4/0 paper on a more standard (CAMI/FEPA/micron) measure?

4/0 sounds like it's 4/0 _emery_ paper. Looking that up, http://www.cafa-info.org/grit.html says P1200; I'd had it in my memory at P2000, however, and can find informal support for that. Somewhere in that band for sure.

This is a rather old designation about which I could find no precise data.
This polishing paper was used some 40 years ago in a military ammunitions plant I where I worked at the time. It was used dry for the final polishing of the dies used in making brass shells, and wet for the final polishing of metalographic samples of heat treated tool steels (although it doesn't stand water well, being paper-backed).
Recently I could find a number of sheets in grades 2/0, 3/0 and 4/0 in a small store, where they were glad to get rid of them, as they had held them in stock for years

The only way I have of relate these grades with any current standard is by a very rough sight and polishing results comparison. The finest grade I can get now is P2500, which has a nominal granulometry of 8.4 micra. This gives results roughly comparable to the above 2/0-3/0. So I assume 4/0 is probably on the range of 5-7 micra. But, as I said, it is a very rough estimate. If someone could find a reliable source of information on this standard of grading, I would be glad to know about it, just out of curiosity.

Can you disclose any more about the stone history? How does it smell when wet? Does it get blackened quickly with swarf? Does it slurries easily? Any pictures of slurry? If you can try can you put a drop of vineagar on it and check (best with some magniffication) if it makes bubbles? Any cracks or original chips in it? If yes can you show picture of them?
I know many questions but all of those can change the result. At present I am between manmade hone and Travertine.

No perceptible smell, wether dry or wet, at least that neither my wife or I could feel. Does not get blackened quickly when used with water (but it does blacken rather quickly when used dry). The slurry is the same colour of the stone, not very perceptible in a picture, so I took a picture of a bit of sandpaper with some slurry on it (sorry for the poor quality of the pic). BTW, the stone appears much closer to the real thing in this picture than in the previous one, which had a greenish tint. The actual colour is light neutral grey. No visible reaction to vinegar, so probably not a calcareous rock. It requires a definite pressure to be scratched by a fingernail, I would rate it at 2 or 2-3 on the Mohs scale.

Thank you people for the replies so far.

 

[adrspach]

From what you described now I am more close to say it is manmade hone.

 

[bugbear]

It requires a definite pressure to be scratched by a fingernail, I would rate it at 2 or 2-3 on the Mohs scale.

Careful - it's possible to have very hard particles in a soft bond (to use synthetic stone jargon).

BugBear