I like hairspray. I’ve never had much luck with Elmer’s glue — white or gel always leaves evidence behind . I’ve also used aloe vera (tip from Petra Kaiser) and Klyr-Fire. I took a class recently from Janet Schrader, and we used clear nail polish. Seemed to work OK, and once dry, it certainly holds. I would run some tests on transparents, though.
Jester’s Baubles Fused Glass Designs