It's incredibly easy to make Jell-O™ or other gelatin glow under a black light. Here's how to make it happen:

package of Jell-O or other gelatin

tonic water

black light

Make the Jell-O

Follow the directions on the package, except use tonic water instead of water. For a small package, the usual directions would be to heat 1 cup of tonic water to boiling. Mix the boiling tonic water and Jell-O until the powder is completely dissolved. Stir in another cup of tonic water. Pour the liquid into a pan or bowl. Refrigerate the Jell-O until is has set. You can use cookie cutters to make shapes out of the gelatin if desired. Shine a black light on the Jell-O to make it glow.

No matter what flavor/color of Jell-O you use, it will glow bright blue under the black light. This is the fluorescence of the quinine in the tonic water. Quinine also gives tonic water a distinctive bitter flavor which you will also taste in the gelatin. If you don't like the taste, you can lessen it by using half tonic water and half tap water in the recipe. Either sugar-free or regular tonic water works fine for this recipe.

Some recipes call for using a low percentage of tonic water (5-10%). The glow from this gelatin will be extremely faint, especially if the dessert is colored. You need a decent amount of quinine to get a bright glow.