Hey Doc, I'm afraid that I can't help you when it comes to the "Vitrea" glass paint that you are using. But I can tell you that when ever I have a new paint that I'm not comfortable trying in one of my better Double Action brushes.
I break out one of my Paasche H Single Action brushes. That brush is inexpensive, extremely simple, and easy to clean up. I have shot a lot of different stuff out of these brushes with pretty good results. Of course I'm assuming that for a stained glass effect on the glass surface is not going to require a lot of detail.
Someone will probably follow shortly with their experience with "Vitrea"