Eureka, it works!

I have read about people using Elmer's white glue to create privacy film on their windows either rolled on by itself or mixed with food colouring to create faux stained glass windows. But, how do you clean your windows?
I have read about using specialized (and expensive) masking liquid to make window frame painting easier. And I have a LOT of multipaned windows and doors that need to be painted inside (outside is done).
I also have a gallon jug of Elmer's white glue that I bought for another project. So...
I poured a small amount of the glue on a plastic plate and used a small 1 inch foam brush to "paint" the inside edge of a few squares of the window frame. Not neatly and did two coats one inch wide. Let it dry overnight and then scored the glass on the inside frame edges with a razor blade and a ruler. Bingo! Peeled right off easily, in one piece. WAY cheaper than the masking liquid and much quicker than using green painter's tape.
Easy, I love easy!

Remember covering your hand with white glue when you were a kid and peeling it off when dry to get a hand "skin"?

I actually never use masking tape when painting window frames. Not much gets on the glass using a small angle brush if you have a steady hand
I just use a razor knife to cut and scrape off any paint that does get on the glass.

But using the white glue, the job might go faster, as you don't have to be that precise.