As for lapping compound, I use Copper bottom cooking pan cleaner...it's an extremely fine white (liquid ) polishing compound. You only need about a drop, at most.

I don't know 'bout you guys, but I have several X-Acto knives with #11 blades in various states of dullness (is that a word? "dullness" )
I use the dullest (least sharp?) one that has just the very the tip broken off, and very carefully scrape the carbon off w/ that....then polish the valve head and stem w/ 1000 wet/dry paper and light oil.