Tumbler media -cob meal?

Hi and what does the cob meal do for the piece?? If it is to dry
why not air pressure???In a class I took with Michael good we
used the air compressure to dry things and that way we didn’t get
marks or etc. on the metal after the tumbler.or buffing
etc…Hope that helps but still want to know about the cob meal
and also what is the red buff…I thought you might mean to buff
the piece again with rouge??thanks calgang