YouTuber PhotoAndGrime.com (real name Pieke Roelofs) has put together a very cool tutorial on how you can take some simple store bought ingredients, blend them together, and BOOM! Suddenly you have UV reactive fake blood!
The process is very simple: All you need to do is chlorophyll pills and some kind of cooking oil, such as olive or canola. Blend the two for a long time until it’s as smooth and liquidy as you can get it and then strain it. What you’re left with is a green liquid that turns into this really cool red that glows underneath a blacklight. Here’s a bonus feature: this is 100% edible, although due to the taste you’re going to want to put it in with something sweet.
If you’re planning on doing a Halloween rave, this is definitely a very cool trick to have up your sleeve.