So, two questions for discussion:

1- What are peoples opinions of hand lapping valves. Used and/or freshly ground. And by hand lapping I mean, compound goes on valve, power drill spins valve while tapping against seat.

2- How is valve seat to valve seal checked using a spotting agent like Prussian blue/HiSpot Blue? Without being able to control film thickness I dont see how you can know what sort of seal you're getting. Maybe something like a permanent marker would work better because it would seem like its film thickness would be extremely thin and more consistent, but it dries so fast that might be an issue.