Grinding and Sanding
It is always interesting to see what the local solution to sharpening is as it is a common problem.
Many parts of the world have sandstone which will work reasonably well for crude sharpening, not all sand Is very sharp though.
In volcanic areas there is often very hard rocks and soft ash formed rock.
A slurry with sharpening properties can be made by using the hard rock as a base and adding water to crumbled soft rock.
A bit of emery cloth works well.
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