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Explore Glow-in-the-Dark Water!

44 reviews


Active Time
< 10 minutes
Total Project Time
< 10 minutes
Key Concepts
chemistry, water, light, fluorescence, energy, ultraviolet light
Teisha Rowland, PhD, Science Buddies
Tonic water in a cup glows fluorescent blue under a black light


Have you ever been fascinated by things that glow in the dark? It can be a lot of fun to play with bracelets, wands, and other toys that are glow-in-the-dark, like some stickers and creepy, crawly, plastic insects! Have you ever wanted to make something at home that glows? It turns out that it is not that hard to do — all you need is tonic water and a black light! Some common household chemicals can also affect this beverage's glow. In this science activity, you will make tonic water glow by using a black light, and then you will add a little bleach to the water. How will adding bleach affect the glow of the tonic water? Try this activity to find out!
This activity is not recommended for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.


  • Tonic water
  • Clear, plastic, disposable cup
  • Medicine dropper
  • Optional: Measuring cup
  • Bleach
  • Ultraviolet "black light"

Prep Work

  1. When handling the bleach, be sure to read and follow all safety precautions listed on the container. Adult assistance is required when handling bleach. Do not drink the bleach or the tonic water mixed with the bleach!
  2. Avoid looking at the ultraviolet "black light" and shining it on your skin as the light can damage your eyes and skin.


  1. Pour about one cup of tonic water into a clear, plastic, disposable cup.
  2. In a darkened room, turn on the ultraviolet black light and shine it on the cup.
    Think about:
    What happens to the tonic water in the cup when the black light shines on it?

  3. Use the medicine dropper to carefully add two drops of bleach to the tonic water. Shine the black light on the cup of tonic water and carefully mix the bleach in with the tonic water.
    Think about:
    What happens when the bleach is added to the tonic water? What happens after the bleach is mixed in with the tonic water?

  4. If you do not see a change in the tonic water, try adding and mixing in a few more drops of bleach. What happens?
  5. If you have some left, under the black light you can compare the glow of the tonic water in the original bottle to the tonic water that had bleach mixed with it.
    Think about:
    Do they look very different? Overall, how did adding bleach to the tonic water change its glow under the black light?


You can pour the very diluted bleach down a drain. Thoroughly clean anything that came in contact with the bleach.

What Happened?

You should have clearly seen that the tonic water glowed a brilliant, bright blue color when you put it under the ultraviolet black light (before adding bleach). This is because the tonic water contains a chemical called quinine, which can absorb the ultraviolet light from the black light and then release (or emit) blue light. After adding and mixing in a few drops of bleach with the tonic water, however, it should have stopped glowing. What is going on? Bleach is an oxidizing agent. As an oxidizing agent, bleach can disrupt and break certain chemical bonds. These chemical bonds in the quinine are the ones that absorb the ultraviolet light. This means that by adding bleach to the tonic water, the quinine becomes unable to absorb ultraviolet light any more, and so it can no longer emit blue light.

Digging Deeper

Tonic water is a carbonated beverage that has a chemical called quinine dissolved in it. Quinine is from the bark of a tree and has been used for centuries as a treatment for malaria. Quinine not only gives tonic water a characteristic bitter taste (which was offset by mixing medicinal tonic water with gin by the British to create gin and tonics, and is offset today by the addition of high fructose corn syrup to bottled tonic water), but this chemical can also be very fluorescent under the right conditions.

Under an ultraviolet "black light," the quinine in tonic water makes the water fluoresce a brilliant, bright blue (even though a relatively small amount of quinine is dissolved in the water). In general, something fluoresces because it has absorbed light energy, which makes it excited, and then it releases (or emits) light as it returns to its normal, un-excited state. Part of why we find things that glow under ultraviolet lights — like some minerals, fish, and tonic water — to be fascinating is because we cannot see the (ultraviolet) light they absorb, but we can see the visible light they emit (which is blue in the case of quinine).

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For Further Exploration

  • If you dilute tonic water with regular water, you can make the tonic water glow less brightly. How much tonic water is needed (if you dilute it with normal water) for it to still visibly glow under an ultraviolet black light?
  • Bleach is a type of chemical called an oxidizing agent. Some other common, household oxidizing agents include hydrogen peroxide and Oxiclean (which contains sodium percarbonate). When other oxidizing agents are added to tonic water, do they have the same effect on its glow under an ultraviolet black light that bleach does?
  • You could try preparing JELL-O with tonic water instead of regular water. Does the JELL-O made with tonic water glow under an ultraviolet black light? (Tip: Try preparing the JELL-O with water that is hot but not quite boiling.)

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