UN-paint my car? Raw panel as final aesthetic? (Art-car)

[300Drestoration]

I'm considering all cosmetic options for my 1985 300d that is close to being finished in terms of operative restoration.
I recently needed to buy a glass bead media blasting setup for work related endeavors where I remove old powder coat from aluminum sheet metal and ive been quite pleased with the resulting rough yet brilliant appearance. So it occurred to me that I could use this rig to do the same to my mercedes. Im already up against a major obstacle to re work the cosmetics since there is significant rust and some dents.
Obviously I could blast the whole thing and consider that the starting point for primer and painting, but I'm also close to calling this an "art car" and doing it all for total fun and just running with creative impulses. Save lots of time and money too.
But what does rain do to completely unpainted panels? What is the base material.. aluminum? What would happen over time?