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how well did you clean the stone after use? the corners usually do not get used in honing while the rest of the stone may very well show the greyness of use.

they also could be showing remaining...

try a little chlorine bleach in the water to keep the slime away

i either placed mine in the dish rack overnight to let it get fairly dry then put it int he plastic case... the other method it to keep it soaking all the time... depends on how much you use it

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