When I was a kid, occasionally my aunt would get these decorative kits from the craft store which were meant to mimic a stained glass piece. they had aluminum frames cast into the shape of whatever it was supposed to be (flower, house, etc.) to simulate the lead cames and baggies of clear plastic pellets of various colors. You put the metal frame on a baking sheet, then filled the various compartments of the frame with the colored plastic pellets, and baked it in the oven to melt the plastic and out popped something which looked like a stained-glass piece.
anyone remember what those were called? This would have been from the early '80s or so.
I don’t know if there is a name in general, but I’m sure one of the brands was called “Makit & Bakit” (when I cleared out my mother’s house after her death I had to dispose of dozens of jars of those leftover ‘crystals’ from her Girl Scout troop days.) Googling that might work.
There’s also another style of stained glass thing now, where you paint with semi-transparent PVA-based paint onto a plastic sheet, then peel it off and stick it onto the window. That one’s rather nice, because you can do any image you like.
I had a similar nostalgic pang a decade ago and made the same discovery that you did. All the interesting Makit Bakit kits from my youth had been replaced by ponies and rainbows. I ended up finding someone selling a bunch of old kits from the 70s on EBay and bought them so I could make Christmas ornaments with my kids.