I know it ain't paint but here's what I did.
I have a clear glass shower enclosure. After years of "soap" scum build up it appears that none of the consumer bathroom products that the wife has used was even able to make a dent. So yesterday I broke out the trusty PC, an orange LC 5.5" pad and the M105 and went to work. (No, I didn't follow up with M205. It's glass not paint.) :
"You can't do by hand what you can accomplish with a machine."
I removed the bypass doors and laid them on the bed.
This allowed me a flat surface to work on 'em. I used the PC on speed 5, 15 lbs of pressure and slow "inch per second" arm speed. I just kept thinking Kevin Brown Method as I was watching the backing plate mark rotate. There were a few tough "spots" that I had to crack out a Megs microfiber cutting disc to remove them.
NOTE: Hard "bad" water can cause non-removable stains in glass just like in can paint but I was lucky and this had not happened.
The glass came out crystal clear!!!
All those years of build up were gone! The only "difficult" spots were the very small areas in the corners where the PC could not reach. I did these by hand with some M105 on a MF towel. (Yes, I used a cheapy MF towel) I even spent a little time and polished the aluminum frame using the PC. The PC also clean it off the aluminum and gave it a great shine.
OK, now on to the detailing 101 follow up.
Like all polishing it's a job and I didn't want to have to repeat this process any time soon. So after I did an IPA on the glass I reached for a sealant. I didn't want to use a wax as it may look a little foggy/smeary on clear glass and I wanted something that would last against daily water and be very hydrophobic.
Bottom Line...the wife came home and was amazed at the results. (and I found a use for the PC that she liked)
You know...I'm not really sure if she was more amazed at the results or the fact I did some "extreme" housework.
So my advice is...If you want your wife to approve of your "hobby", polish the shower doors & use an LSP sealant.
BTW - The glass block window is not in the shower. It is actually a reflection in the glass.