Hand Tools Archive
I can comment on the dry diamond side. A tiny sprinkle of the diamonds and a few drops of WD40 is enough for them pretty much to spread all over the place.
(this is for fine diamonds).
when the WD moves around and is milky because of the diamonds, you know they're getting everywhere. They're cheap enough now that it doesn't matter that much if some are wasted (talking $10 a year for heavy use of several fine grits cheap).
Eventually like stone slurry, it darkens. You can push some of the slurry away from an area on the stone or surface that you're using and then run the bevel of the chisel over the cleared area. It will darken the surface quickly, you're good to go until the surface isn't darkened quickly. This is easier on corian than cast, because the cast can do a little bit of work on its own and is about the same color as swarf.
I've only used large loose diamonds on a mild steel plate, and that wasn't ideal, so I'll defer to bill on those. They rolled on the steel plate for a while and the whole shebang worked better with a bunch of rolling diamonds, but that's far from ideal (they're abrading the substrate and the object to be ground at the same time).