Thread: Grain in Charnley Forrest stone

I just procured another CF stone by accident! (thinking it was something else) I'm not unhappy with the result but the very small size of this one made me think it may be particularly fine and intended originally for honing razors. It is very smooth indeed. I wanted to compare it to my other CF stones as I know these do vary. I used the tongue test as I often do (after a good clean) and I found that there was a big difference in sensation on my tongue if I moved it lengthways or sideways on the stone. This leads me to suspect that there is a natural grain in this stone and maybe to get the best finish / slowest cutting action the grain should not be aligned with the length of the stone, but with the width. Has anyone else noticed this?

How does the edge compare with the your other CF?

That's interesting.
I know it happens on the phyllite containing whetstones, a few slates, and generally, on minerals-stones that have a binder, and the abrasive particles are quite big sized but thin, able to break in pieces easily. If you follow the grain, they might be coarser, but vertically, their scratch pattern gets smoother. Or something like that.
There are very few stones that have this characteristic, almost none of the famous finishers.
The reason this doesn't happen in the Charnley forest stones is, the whole stone is a single particle. There are no pores, and Charnleys are not famous for their cutting ability, more like the opposite. They don't have cutting particles, like Thuringians and coticules. The roughness or smoothness of the stone surface is what cuts. Like a piece of glass, hard enough to scratch steel, but there is no grain. You can lap it with coarse sandpaper and it will cut fast and deep. Or you can use it as you buy it with a smooth surface, where, it will be smooth, extremely slow and pretty much useless.
I'm still trying to figure out what is going on with those things, so I would be interested to hear from other members too.

Thanks for your response Vasilis. I just looked under a microscope and could not see anything in the structure that would make this make sense. I think that what I was feeling was the direction of my lapping strokes. This could explain the directional feeling on my tongue and also is supported by your great description of how these stones work.

To me you already found your answer. It is quite natural that people lap their hones more one direction then others and it can leave adequate pattern on the hone.

I think that there are a few misconceptions being propounded here regarding CF hones - why, I don't know, as all the info is on this site in various places and I feel sure that most of us interested in these hones have read it already.

The main composition of a CF is novaculite - the same finely divided recrystalised abrasive found in lots of other natural stones like Arkansas, Hindostan, Turkey Oilstone, etc. Not only is it an abrasive particle (99 per cent silica) but it exists in hones in a range of sizes, although it would be hard to see much at anything less than 500 - 1000x magnification. The fineness of the cutting action depends on how the abrasive particles are distributed in the matrix of the hone - if they are very close together and fine and if the matrix (ie the groundmass of the stone in which other particles are ingrained) is of a similar hardness to the cutting particles the hone will cut slowly and finely. If the cutting particles are large, sparsely spread throughout a soft matrix, then the hone will cut fast and coarse.

Originally, the deposits that formed CF hones and other novaculites were sedimentary, and this means that we get all the variety that can be expected from rocks laid down in such a way, including inter-bedding of other deposits and inclusions and strata from various other sources. Quite clearly, the characteristic colourful CF with its mossy green shades, red streaks veins and swirls and black dots is not a 'single particle' type of rock, neither is it poreless - plenty of the darker areas present cavities on closer inspection, pores and hard crystalline inclusions ('pinny' masses) that are harder than the rest of the rock and which must be removed if we are to avoid scratching the razor.

Some forms of the colourful (as opposed to the drab) CF hone also exhibit the phenomenon of chatoyance, or cat's eye effect that is associated with certain types of stone. This gives a kind of 'depth' or 3D effect to parts of the surface, where we can almost 'look' down into the stone and see what appear to be fibrous layers or inclusions. Not that there are fibrous structures there - the effect is due to the grains or crystal structures and other chemical deposits being laid at different planes or axes.

In some CF hones this change in orientation can be felt, as can areas of inclusions and other stria. There is no doubt that lapping to a finer or coarser feel will affect the honing characteristic of the hone, but these other natural deviations will also be present in some cases and are not due to how the hone is lapped.

Just one final thing with regard to CF hones - in none of the 'detailed' literature about their use is it implied that they were expressly used for honing razors. They have been mentioned in association with razors, sure, and for fine edges on carpenters tools, but the most detailed reference on there use (Holzapfel, I think) declares that they were merely used to strike-off the feather-edge left on a razor bevel after it had been set (ground) on a wheel. Not that they don't give a remarkably fine edge - most of them do - but they were slow and hard and glassy, the last two qualities making then suitable for striking off feather edges. I suspect that people honing razors by the score for factories back in the day made use of something far faster!

Regards,
Neil

Thanks Neil. I hadn't pulled all the info together, so thanks very much for taking the time to share this.