[M_D]

I don't know exactly what your parts look like, so this may or may not apply.

One type of grainy appearance is from metal removed in the etch or bright dip process, which brings out the grain of the metal. There will be very small dark steaks oriented with the grain. The longer the etch, the more the grain will become pronounced. It is more ovious on bright shiny surfaces than on duller surfaces.

Also, the parts may have been stripped and re-anodized. Stripping with a sodium hydroxide (lye) stripper will tend to leave a spotty, galvenized look, which is still obvious after anodizing. Also, etching too long will do the same thing.