Glowing Water & Oil Mixing Experiment (Taste-Safe!)

Published: May 7, 2020 · Updated: December 30, 2023 by Sacha — This post may contain affiliate links. Read our full disclosure.

Amaze your kids with this cool, glow-in-the-dark version of the classic oil and water mixing experiment. And since all the ingredients used are taste-safe, you don’t have to worry about your little one ingesting harmful substances!

Did you know that tonic water glows under black lights? I had no idea until recently!

I love glow-in-the-dark experiments, but we have a two-year-old at home who puts just about everything in her mouth, so I was a little worried about using glow-in-the-dark paint or pigment around her. The fact that we can now do these activities using edible ingredients is such a relief!

This experiment is super simple and easy to set up, but the glow-in-the-dark aspect adds a really fun twist to a classic. Use it to talk to your little scientist about how oil and water don’t mix!

Required Materials

Here’s what you’ll need to do your very own glow-in-the-dark water and oil mixing experiment using taste-safe ingredients:

Supplies needed for this glowing water and oil experiment.
  • Cooking oil (use coconut oil for best results—it’s pricier, but you won’t need a lot)
  • Tonic water (important note below)
  • Black light
  • Small containers
  • Droppers (we bought ours on Amazon, but I can’t seem to find an equivalent product anymore—just make sure to use plastic instead of glass if your kids are young and/or accident-prone)

Important: The brand of tonic water you buy must list “quinine” as an ingredient, since this is what causes it to glow.

Bottle of tonic water, showing the words "Contains Quinine".

How to Conduct a Glowing Water & Oil Mixing Experiment (Step-by-Step)

1. Pour Tonic Water & Oil

Start by pouring a little bit of coconut oil into one container and a little bit of tonic water into another.

2 small containers filled with tonic water and oil.

Note: I had to place the coconut oil in the microwave for a few seconds to melt it, because I live in Canada, so my coconut oil stays solid for most of the year. Yours might already be liquid if you live somewhere warmer.

In the picture below, I shone a black light onto the two containers, and as you can see, the container of oil on the left doesn’t glow, but the container of tonic water on the right does. Perhaps I’m easily excited, but isn’t that so cool?!

Black light shining on a container of tonic water and making it glow in the dark.

2. Combine Tonic Water & Oil

For the next phase of the experiment, use droppers to combine the oil and tonic water.

Dropper adding drops of oil to a container of tonic water.

You can combine them both in a separate container, but it looked the coolest when we poured little drops of tonic water directly into the oil. It won’t look like much under regular lighting, but if you turn off the lights and shine a black light onto the mixture, the drops of tonic water will begin to glow!

Water filled with glowing oil, in the dark.

Since oil and water don’t mix and tonic water is mostly carbonated water, the drops of tonic water will float around in the oil. And since oil doesn’t glow under black lights, only the drops of tonic water will light up!

Which Type of Oil Should You Use?

Coconut oil works best because it’s clear, so it allows the black light to shine through and reach the tonic water. It’s more expensive than certain other types of oil, but we only used about a tablespoon for this experiment.

However, if you find the cost too high or don’t have any coconut oil on hand, you can always use another type of oil, such as vegetable oil. I tested it and got these results:

Water filled with glowing oil, in the dark.

I’m not sure whether it’s clear from the picture, but the tonic water didn’t shine as brightly because vegetable oil isn’t clear.

If you want to use clear oil but don’t have any coconut oil, you could also use baby oil. But keep in mind that if you do, this experiment will no longer be taste-safe. This is not a big deal for older kids who know not to put things in their mouths, but if you’re scared that you child will try to ingest the baby oil, you’re better off sticking with some form of edible cooking oil!

Related Taste-Safe Activities

Looking for more taste-safe activities to do with your little ones? Check out these articles:

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