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I'll take that bet!
I've had more than one that was far from flat, the last a privative from Dan's was way out. Took quite a bit of work to remedy.
I never new just how uneven and (not flat) my...

For starting out I recommend Balistol or Glycerin as you can dilute these w/water to create a thinner medium, encourages experimentation and they both work well and clean up easily.
I've had similar...

ScoutHikerDad:

I sent you a PM.

No, these stones are not porous so you can wash them before storing.
How you prep the stones surface once flat has quite an effect on how the stone may behave, yet another way to experiment.

As to your questions. If you hone up the progression w/tape you will need to finish w/the same to keep the edge angle consistent finishing the edge of the previously established bevel.
As far as...