So I reverted to Plan B: heating the metal to create a patina-like surface. However, this also has the same flaw in that because they're not actually those metals, they don't react and "tarnish" the same way real copper or brass would. As a result that was a failure too!
The end result was that I turn to the old standby of just using paints and washes to achieve the desired patina. I think washes of greens, blues, and black created an effect that this is an aged holy water font.
After completing that task, which took a surprisingly long time to achieve, I turned my attention to the stained glass window. I completed outlining the design in the grouping of three circles then began painting the images in the lower windows.
Okay! This was actually a lot of fun to do. Admittedly it was a bit tedious, but painstakingly plodding along helped move the project much closer to completion. I think when the window is painted and installed, and the lighting is put in behind it, it will look like a real stained glass gothic arch window. Check out this artist's stained glass window, and you'll see the effect I'm talking about with the window lit from behind with rope lights:
So far I'm very happy with the project's progress, but of course, there's more to do on this window as well as on the second one. So this project is not yet one for the books.
However, I plan to begin working on the candle offering luminary table, doing both projects simultaneously (for my sanity as well as that of those tagging along and following my progress int hat they don't have to just watch me paint small areas on the stained glass window).
I think I have a workable solution to what could have turned into a major project, but unnecessarily so.