After years of use, the black paint on the frames will be worn off in places. To restore the new look you first need to prep the metal with phosphoric acid so the paint will adhere. Jasco Metal Prep (phosphoric acid) may be available at your local big box store. [Note, it was not available at my Lowe’s or Home Depot and shipping it was going be costly because it’s now deemed hazardous. You might find it at paint store frequented by pros or at a business that installs tile. So good luck finding it] I remembered that I had a jug of tile cleaner and found it was phosphoric acid.
I would suggest doing this project when the temperature is around 70 and humidity is low. Take care that the temperature of the window frames are also around 70-85.
You probably will want to cover any fabric in the work area first.
If you have sensitive hands, wear gloves.
Apply the acid with a q-tip and let it dry for 30 seconds and wash it off with water saturated clean rag.
I used Rust-oleum gloass black paint. It needs to be thinned – quite a bit – so the finish will be smooth. I used q-tips to apply the paint. Apply sparingly.
All credit is due to bumper and SoCal Larry