How to remove Hammer Finish from aluminum

I have this old theatre lamp: Attachment 37394 (http://www.doityourself.com/forum/attachments/painting-staining-all-interior-exterior-surfaces/37394-how-remove-hammer-finish-aluminum-strand123.jpg) It has a hammer finish on it (a kind of coating). I wish to remove this coating from the aluminum shell. I tried polishing it of with metal polish, which works but takes forever (even with a polishing machine). I also tried removing it using "rust-oleum" which is supposed to be very good but (I gues because its a coating) it doesn't work. Does anyone have an idea to remove this coating without harming the aluminum (I want to polish it to a shiny finish later on).