How To Paint Molded Mullions
by Tom Gloger and others
(Atlas Model Railroading Forum)
Tom Gloger came up with a technique for painting the glass window mullions of this Walthers kit:
I took a rubber eraser, the pink kind with the trapezoid cross section, used to be called Pink Pearl, set it on my work table and applied a layer of paint to the top of it. Then I took the window casting and pressed it down into the paint.
If you use too much paint on the eraser, it is possible to get some on the window pane, so take it easy, don't try to rush.
Because the window castings are clear, you can look through it to get some idea how much paint you're getting on the frames.
When done, I picked the best ones to put on the aisle side of the building.
I was painting them green, and IIRC it took two coats to get good coverage. Also IIRC, it took about half a bottle (the smallest Poly-Scale size) to do all the windows in the Walthers Car Shop. A lot stays on the eraser.
A tip about the Back Shop and Car Shop: With all those windows and skylights, you may want to paint the interior walls before assembly.
As an alternative, you could use a hard rubber ink roller, mount the windows flat on your work surface and hold in place with double-faced tape. Spread paint on a flat surface (glass, plastic, or metal). Now pick up a coating with the roller and gently roll the roller over the window without pushing down too hard.