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A shellac based hone is best lapped by using a wet/dry sandpaper whetted with a lot of water, and keep it very wet.
Use very light pressure, almost none. It will take a bit of time to get it flat...

I also have one and also have not used mine yet. But...Robert Williams ( Papabull) has used them and likes them.

Note that on the box it says distributed by Peter J. Michaels. well, they did not...