What in the manufacturing process gives aluminum foil a shiny side and a dull side?

Answer 1

Two pure guesses.
1) There are calendering rollers (very smooth chrome finish) where contact with the web is intended to leave a smooth high gloss finish on the contact side and the non-contact side would be relatively less glossy by comparison.

2) Chemical treatment of one side (eg antistat or a release agent) would reduce gloss on that side

I am not familiar with the process but those are my thoughts.

Answer 2

see: http://en.wikipedia.org/wiki/Aluminum_foil

Foil processed two rolls at a time. The sides that are in contact with the other roll's foil is not shiny.