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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.

  • Start with the coarser and finish with the smoother. I am sure there are videos on you tube. – paparazzo Aug 3 '16 at 18:01
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    @Paparazzi ... how can the user start with the coarser if they don't know what coarseness level they are... that's the entire point of the question. – Catija Aug 3 '16 at 18:26
  • @Catija You don't have to know the actual coarseness to know if one is more coarse than the other. It will feel and look coarser. – paparazzo Aug 3 '16 at 18:30
  • But that is not what your comment says. It may be that you intended it to mean "start with the one that feels coarser to you" but what you typed doesn't necessarily say that. Regardless, if you're trying to answer the question, do so in an answer, not a comment. – Catija Aug 3 '16 at 18:31
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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 '16 at 18:31
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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.

  • Unknown, cheap stones are usually great for flattening the better ones :) – rackandboneman Aug 19 '16 at 14:51
  • Use caution: I’ve had the coarse grit contaminate the fresh surface of the flattened stone. – JDługosz Aug 19 '16 at 15:33
  • 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 '16 at 15:35
  • So not waterstones. I know the one you mean: $2 at the restaurant supply company. – JDługosz Aug 19 '16 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 '16 at 15:40
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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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