I can't tell for sure from the picture, but my guess is part of what you're seeing is micro bubbles/scum from the frit. I haven't worked with maraschino so don't know the color well or if it reacts with different glass. But I think part of the color "change" you're seeing is the micro bubbles clouding on the surface of the red. I would not recommend using frit for encasing. maybe try doing the same thing with another opaque color and see if something similar happens. My guess is, it will.
Mimi
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