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I've received a few sharpening stones with different coarseness and even one double-sided two-colored stone. Is there any way to tell how coarse each stone is and which stage of sharpening it would be appropriate for? I'm not experienced in sharpening and I'd like to learn.

I was suggested to mark the edge of something made of metal (not necessarily a knife I'd like to sharpen) with a black marker and slide it once across each of the stones, make a macro photo of the removed black paint and compare the scratched areas. Is this a viable method? I don't have a macro-capable camera so I can't try it myself.

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    problem is my stones are not radically different from each other, and I can not tell apart 3 of them :/
    – user1306322
    Aug 3, 2016 at 18:31
  • A fine stone could feel coarse if the surface got roughed up, a coarse one could feel very fine if it got glazed over or polished. Good medium and fine stones often all feel rather smooth to the touch anyway...
    – rackandboneman
    Aug 19, 2016 at 14:54
  • BTW, good sharpening tutorials on YT: Anything by Jon Broida, anything on the channel of Korin Knives, anything by Murray Carter, anything by Mino Tsuchida. Yes, these are done by people that are in the knife business. Professionals.
    – rackandboneman
    Aug 19, 2016 at 15:00

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With some experience you can tell by running a finger over the surface.

As a general guide:

  • grinding stones used for serious repair of knives form damage of long ngelect; will feel disticly rough, not as rough as sand paper but you can definitely feel an abrasive surface.

  • sharpening stones : these will have a smooth surface but will have a definite 'drag' or friction to them, a bit like rough paper. These are used for normal sharpening of knives.

  • Polishing/finishing stones : these will feel very smooth with just a hint of texture, a bit like magazine pages. Used for refinement and polishing of a cutting edge .

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There’s more to it than just grit size and there are complexities that won't show up in your marker test.

What kind of material are they made from? Are they intended as water stones or oil? The waterstone is the hard mineral mixed with weak clay so it comes off and makes a slurry when you work it. On the opposite end are ceramic or metal stones that don’t wear at all but are meant as a permanent surface holding the hard grit (typically diamond).

Of the non-permanent type the amount it’s supposed to wear will vary, and the resulting slurry may be more or less friable, meaning the actual effective grit size changes as you use it!

So, unless they are all the same type meant to be used as a set, you can’t tell anything.

You just have to know the technique appropriate to that kind of stone (oil or water? Work up a slurry or keep it clean?) and get a feel for what that particular stone does for you.

If you don't already know sharpening I think you should get rid of those unknown stones, or ignore them until you do know more. Get instructions and stones to match that have known characteristics. You'll also need secondary materials like little stones used to prime the water stones, strops and compounds to use on them, guides and gauges for getting the angle just right, a way to dress and flatten your stones, stuff to get gunk out of oil stones, etc.

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  • Unknown, cheap stones are usually great for flattening the better ones :)
    – rackandboneman
    Aug 19, 2016 at 14:51
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    Use caution: I’ve had the coarse grit contaminate the fresh surface of the flattened stone.
    – JDługosz
    Aug 19, 2016 at 15:33
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    Valid point. Most cheap coarse grit stones (and that is what i would assume an unbranded, unmarked stone to be if it comes that way new) are hard as bricks though and lose very little of their material.
    – rackandboneman
    Aug 19, 2016 at 15:35
  • So not waterstones. I know the one you mean: $2 at the restaurant supply company.
    – JDługosz
    Aug 19, 2016 at 15:37
  • Yep :) But honestly, whenever somebody says "oh, I got some whetstone...", it is very likely to be exactly that :)
    – rackandboneman
    Aug 19, 2016 at 15:40
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I had a similar issue, oke I am a little seasoned but not very much. Never the less I found for myself a solution that might work for you or others.

First though I will mention my personal issue:

I have about 10 wetstones of different courseness running from 120 to 2000. Some had markings still, some not. Some were knowingly of the same courseness (so twice) Some were of different (coloured) materials (orangie/white) both probably corundum.

The easiest way to compare the coarseness was by listing to the difference in tone of the material grinding over the wetstone (I took an old knive) the finer the grit, the higher the tone I believe. This gave me an easy comparisment and get me sorted out. Of course it does not give you a value! is only compares..
I need to mention that I am pretty tone deaf, so if I can hear the difference anyone should be able too.

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The way to do some more determination besides "feeling" with your fingertips might be, to scratch your nail across the surface of the stone. Your fingertips (at least mine) will have difficulty determining if you're actually handling a 2000 grid or 4000 grid...with your nails the difference is easily made...just my 5 pence...

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First try cleaning the oil off the stone with some kerosene and a stiff brush. You can soak it for a little while. Then try a flattening technique by taking some wet-dry sandpaper (Gator Power Red Resin 120 or 220 grit works well) on a sheet of glass with some kerosene on it. Rub the stone on the sanding sheet soaked in kerosene in a circular motion to clean and flatten, rinsing with kerosene as you go. I use a small pan to dip the sandpaper in to clean it as I go. After a while it will be clean and flat, exposing the grains of the stone, which need to be exposed anyway to sharpen your tool. With the nice clean stone, use a jeweler's loupe (hand-held lens) of 16x, 20x or 30x to look closely at the grain size. If you could measure the grain size, you could consult a grit-size chart to gauge what you have. But since you will probably not have a way to measure the grain size, you could at least compare it to a stone of known size and get an idea of it. Knowing that natural stones rarely go over 1200 grit, you could at least estimate what you have. If nothing else, you will have learned a lot and had a good time doing it.

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Simple suggestion: take the stones to your nearest knife shop, and ask them. That's really the only way that's likely to work.

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