It's Phosphoric acid.
Iron Oxide (rust) > Iron Phosphate (the hard shiney stuff)
It can be bought at stores like NAPA, etc in small bottles, but it is
fairly spendy (3 or 4 bucks a bottle) but I understand it is available
in it's generic name at chemical houses in 5 gallon buckets for about
the same amount.
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Administrative requests: towertalk-REQUEST@contesting.com
Sponsored by: Akorn Access, Inc. & N4VJ / K4AAA