I lacquered mine before lapping it because I had a feeling I'd have lacquer on the honing surface that would need cleaning away. My feeling was right. I used sand paper so the lacquer wouldn't gum up my diamond plate, then lapped the stone as usual once the excess lacquer was cleared off.

Once it was flat I polished away the diamond plate scratches to 2K, then burnished it by rubbing the surface with the Tomo nagura I was sent with it.

As for the type of lacquer I'll let someone else chime in there. I just used some paint on stuff I had lying around. I figured it was better than nothing.