Here's an excerpt from an article I found that deals with how to achieve different grades of finishes on the #1-#8 scale:
"Because stainless steel is harder than aluminum, you will need to make allowances from the known methods for stainless steel when working with aluminum. The stainless designations are as follows: A #3 finish is generally produced using a 120 - 150-grit sanding belt. A #4 finish is produced using a 180 - 220-grit sanding belt. A #7 finish is a beautiful mirror but with pronounced grain lines, while a #8 finish is generally regarded as a mirror with no grain lines. In the United States, a #8 mirror may still have very light buff lines. A #8 finish from Asia will be 100 percent free of all lines. This Asian #8 is extremely difficult to duplicate or blend to because the final process is different from conventional buffing, thereby leaving no evidence of having been buffed."
http://72.14.203.104/search?q=cache:...s&ct=clnk&cd=2
The author neglects to mention the "final process" that aluminum needs to have done to it to get an Asian #8 finish. Hmm, international trade secret perhaps?