Crisco - GREAT! Everything I ever hang with suction cups fall down - usually in the middle of the night. I've never trusted any glass to suction cups as a couple people gave me small suncatchers on suction cups years ago and they constantly fall. I'll try crisco. I hope it is okay on the suction cup I have on a wooden door.
Susction cups are not at their best on wood, because it's porous. If it's got a good thick coat of smooth gloss paint, with no cracks in it, maybe for a while, but suction cups are best on gllass or metal.