Are you sure that is aluminum? The pistol looks like an Eclipse and they are stainless. If it is, I don't think scotchbrite or anything similar will get it out of stainless. I'd just leave it alone.
It is the Eclipse Pro II, the frame is aluminum and the slide is stainless.
Are you double sure?
Eclipse Pro II You need to post a new photo so we can be overly critical of your work. Don't take all the fun out of this for us...lot's of folks have done the same thing at least once.
I, of course, never have. However, I picked up four or five Pachmayr Widgets
just in case. Yeah right, that's the ticket.
Pachmayr Widget Designed to depress the 1911 plunger tube spring, simplifying assembly and disassembly. Also helps avoid scratching the frame when installing a slide release.