Tamiya weathering powders? Better techniques?

[tomsheehy]

I tried using the Tamiya weathering powders on a recent build, specifically I was trying to add a rust look to an exhaust system.  I painted the pipes first, then applied the rust colored powder, so far so good.  But the powder changed the pipes more to 'gold' than a rust color.  Should I use a different base color.  I tried on some black, and got a dirty black.  Anyway, I let it be for the most part, as it gave it sort of an anodized look.  I did add some Testors rust paint up near the engine, dry brushed.

Any thought or experiences would be helpful.  TIA... 

[tomsheehy]

Nobody???   Buhler???