I am new to using whetstones. As such, I purchased a cheap Whetstone (manufacturer is FULUDM) and used an old cheap knife to practice.

What I've noticed is, the 1000g grit (which is a green stone) seems to generate a paint like substance. My searches online provide 0 results as to what this is.

Is this expected or does this indicate a fault or a poor technique?

My technique? Soak it for 30 minutes and ensure there is a thin layer of water on the top at all times (as per the instructions). Hold the knife at about 22 degree angle (depending on material).

You can see the state of my knife from the Whetstone enter image description here

And this gif should also show the paint like substance generated (sorry it's so low quality)

enter image description here

enter image description here

2 Answers 2


That slurry of grit is actually part of how that kind of whetstone works. It's not only normal, but necessary for it to sharpen properly. On "natural"-style fine sharpening stones, the idea is that you are sharpening the knife using a grit slurry rather than on the solid stone itself. This allows for finer sharpening and polishing than you could get from a stone that does not slurry.

In fact, with this style of sharpening stone, you generally rub the stone hard before even touching a knife to it(video) in order to create a slurry.

I have a two-sided King Japanese sharpening stone, which works like this and is how I sharpen my hand-forged knives. The stone you bought looks like a generic knockoff of a King. How well it actually works is up to you to determine; I will say that seems to be creating a lot more slurry than I'm used to.

  • The Japanese even have separate little nagura stones for the purpose of creating a slurry. And there are quality stones of varying hardness; it mostly depends on technique and style which kind suits you better. Mar 28, 2023 at 8:22

This is perfectly normal.

Both faces 'suffer' from the physical action of rubbing them together, as you sharpen the knife you abrade the surface of the whetstone too.
As the grit is very fine, it forms a paste, which just needs rinsing off after you've finished.

Eventually, you'll wear a hollow where the knife has worn away the stone, just like footfall on an old stairway.

enter image description here

  • 4
    I suspect this "cheap" whetstone will dish out a lot faster than a more-expensive one. But an expensive one that lasts twice as long while costing 5x as much, not exactly a bargain.
    – Criggie
    Mar 27, 2023 at 1:41
  • 1
    You can always un-dish the stone...
    – arne
    Mar 27, 2023 at 7:07
  • 5
    If purchased as a set, there should be an extra plate or stone for re-flattening the stones. This needs to be done to keep sharpening effective. Mar 27, 2023 at 7:30
  • 9
    I believe the paste that builds on the stone is called slurry, and it is very important to the process of honing. Don’t rinse it off.
    – Philipp
    Mar 27, 2023 at 11:26
  • 4
    @Philipp It's called /a/ slurry, and (considered from an engineering POV) it might or might not be desirable. If it is being caused by the binder in the stone failing before there is any significant abrasion to the knife, then it's undesirable: the stone's useless. OTOH, high-quality engineering grindstones have friable grit that cracks during use to expose new sharp edges, it's those sharp edges which have a cutting effect on even hard materials, and it's routine to "re-flat" the stone (using a harder stone or a diamond) on a regular basis. Mar 28, 2023 at 7:04

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