King 8000 grit synthetic Nagura stone
A Nagura stone is ideal when you want to bring up a fresh layer of abrasive material on sharpening stones.
Rubbing this Nagura stone over sharpening stones will create a slurry (mud substance) which is beneficial during sharpening.
Some harder stones can glaze up after sharpening for a while. This gives you a feeling of skidding over the sharpening stone.
rubbing with a Nagura stone will get rid of the glazing.
And restore the sharpening capabilities.