Thanks for all of the comments! The slime icing was really easy. The ingrediant that glowed was tonic water. You have to make sure the tonic water you get says containes “quinine”. Then get some clear piping gel ( found in the cake decorating dept) put the piping gel into a sauce pan and heat till smooth (about 5 mins) then add tonic water. I used about a 1:1 ratio of the gel and water but you can do whatever. After heating the water and gel for another 5 mins add food coloring then 1 tablespoon of plain gelatin. Stir very well until dissolved. Take off heat and let stand till cool. The icing thicken as it stands. If it's not thick enough or too thick you can heat it back up and add more water or gelatin depending on the desired consistency.
This will only glow under a blacklight. So keep that in mind!
Play around with it and keep in mind you might need a few trys to get it where you want it. You also might want to add some sugar before you add the gelatin if there will be a lot on what you are eating, the tonic water is very bitter.
Let me know if any of you have any questions about this when you try it.