Materials needed include a creepy looking clear jar or bottle, a colored highlighter, water, some silicone or hot glue (to seal it shut), and a blacklight (needed for the glowing effect).
The hardest part of this prop is finding a suitable container for it. We purchased this cool looking bottle (along with some others) at a resale shop for about a dollar.
The potion glows brightly when seen under blacklight. I got this idea from a cousin of mine who said that she and her roomates used to put colored alcohol bottles under blacklight in college. The secret is the mixture. Nope, its not food coloring. Trust me, no amount of food coloring could produce a glow like this. Its freakin' amazing. I couldn't even capture its brillince with the digital camera. The secret ingredients are water and the spongy insides of a yellow highlighter. Thats it. Just bust open a highlighter, drop the sponge in the water and wait. After all of the ink has leaked out, just fish out the sponge and throw it away. Cork the bottle and you are finished.