Hi Lee,
Marv gave a pretty good run down. Water with a tiny bit of Dawn is a good wetting agent and keeps the paper from clogging.
I *think* the 600 Windy uses to sand silver is correct, BUT, I *think* he then sprays a final coat of silver before his colors. I know that forever (does he still??) Windy used Sig silver for his substrate and blocking coat. Silver shows every tiny flaw that is in the raw finish. That was why he was using it! When the silver is perfect, there are no flaws in the color finish. The 600 was for rapid removal of material while safeguarding a little bit from sanding through to the base. If you are going to use silver for the color (which is what I gather) then sand that coat down and spray a light coat followed by a fiarly wet one. Apply clear before sanding again. Any time you sand raw silver, it will not look good at all. You will have to rub out clear coats.
Bill <><