Making a cross to look like it is stain glass. I am planning to use gel colors and out lining in black. How do I get the black not to bleed or won't that happen? TIA

I made the lead areas a dark gray out of buttercream and it didn't bleed at all. Worked great with the piping gel.

What about using black or gray fondant for the lines? You could even "paint" the lines with a silver luster/vodka mix after they''re on the cake.