I do alittle glass painting and I don't seal it - some of the paints don't really need it. Enamels should be okay without the sealer - I'm not sure about acrylics though. Maybe someone will have a better answer.

I've used acrylics to paint flowers on old windows and hung them outside on my fence as "garden art." Three years later the paint is still there and in perfect condition. Never sealed it with anything!

I used to sell painted mason jars with the candle on top. After the paint is dry (24 hrs), apply 2 coats of Future Floor Finish. You get it at the grocery store. Nothing will harm the paint after that. It will also leave a very shiny finish.