Glow in the dark piping gel sounds like something worth trying for a cake, but it's tricky to find pre-made products to make it work. The secret ingredient is the quinine in tonic water, which naturally fluoresces under a black light. Coloured piping gel is available at cake supply stores. Add tonic water to the piping gel at home to make it glow, or make your own custom-coloured glow in the dark piping gel from scratch for a better glow in the dark effect.
Measure 2 cups of the piping gel and place it into a saucepan.
Add 2 tbsp of tonic water to the piping gel and mix together in the saucepan.
Check the piping gel consistency with a spoon. If the mixture sticks to the back of a spoon, fill the plastic squeeze bottle with the piping gel and use.
Add 1 tbsp of powdered unflavored gelatin to the mixture (if the mixture is too runny for piping). Warm the gel mixture in the saucepan on a hob on low heat until the piping gel thickens to the proper consistency.
Empty 2 cups of cold tonic water into a saucepan, then sprinkle 2 tbsp of unflavored gelatin to the water. Wait 5 minutes for the gelatin to dissolve.
Warm the mixture over low heat until the tonic water and gelatin mixture is clear.
Add 1 1/2 cups of light corn syrup to the mixture and heat through, but do not boil.
Remove the piping gel mixture from the pan and spoon into a bowl or storage container. Cool the piping gel, then refrigerate until ready to use.
Take the clear piping gel out of the refrigerator. Dip a toothpick into the gel food colouring just enough to coat the toothpick. Dip the gel coated toothpick into the piping gel and mix in the colour. Add more gel food colouring using this method until you get the colour you want.
Replace 1/4 or 1/2 of the tonic water with plain water if the homemade piping gel tastes bitter. Test different gel colourants with the clear homemade piping gel for the best glow in the dark effect.
Do not use straight quinine, a medically prescribed drug in pill form, in the piping gel. Tonic water contains quinine in small amounts so it is safe to use.