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More fluorescent, glowing science fun! This time we made glowing ice cubes, using just one easy-to-find ingredient.
Can you guess what it is? Hint: It’s the same ingredient that we used to make our water beads glow earlier.
Need another clue? You should be able to find it in the drinks aisle of your local grocery store. It has a bitter flavour.
Still unsure? OK, I’ll let you off the hook.
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The secret ingredient is: Tonic Water.
More specifically, you need tonic water that contains a small amount of quinine listed as one of the ingredients. (Most brands do, but just double check). It doesn’t matter if it’s regular or diet tonic water, we’ve tried both and they work equally well, as it’s the quinine, rather than the sugar, that makes it glow. (Although as a side note, we do prefer playing with diet tonic water ice as it’s less sticky…)
You’ll also need a dark room (or dark box) and a black / ultraviolet (UV) light (long wave UV-A ultraviolet light with either LED or blb bulb). You can find them easily online – they are often marketed as dog or cat stain finders. We’ve tried several, and they’ve all worked. Currently we have two of these torches.
What happens is, the quinine in the tonic water ice absorbs the ultraviolet light, which is invisible to the human eye, and then emits it back at a visible wavelength. Or, in other words, invisible light goes into the tonic water ice, and comes back out as visible light. Cool!
And it really, truly does glow!
Have a look below at the difference between the regular water ice and tonic water ice. I took these photos in one of my kids’ black canvas toy boxes, which I’d turned on it’s side, as an easy way to create a very dark backdrop. The first image is with natural light hitting the ice cubes from our laundry window. You can just make out that the tonic water ice (in the middle) is slightly whiter and less transparent than the regular ice (on the sides), but essentially they all look similar. (The ice cube moulds were slightly different shapes, but otherwise….)
Now have a look at what happens when I close the laundry window and turn on the black light torches.
The UV light is hitting all the ice cubes roughly equally here, but you can really see that the tonic water ice cubes have a strong blue glow (they look like they are emitting blue light from within), whereas the regular ice cubes just reflect a slight violet tinge.
Fun Science Facts
A black light shines a special type light (called ultraviolet light) which has a wavelength that humans can’t see. It’s like invisible light energy. Things that fluoresce (such as the quinine in our tonic water ice cubes), absorb this invisible ultraviolet light energy, and reflect it back, except this time at a wavelength that humans can actually see. That’s why it looks like it glows.
Quinine is highly fluorescent, even in low quantities. (It’s so consistently fluorescent that it is used in photochemistry as a ‘common fluorescence standard’.
Regular ice cubes just by themselves are a fantastic open-ended sensory play material that kids love. It’s cold, it’s wet, it’s slippery! You can stack them – can you build a tower? Add water, and it floats! When it melts, it turns from a solid into a liquid. You can eat it – what does it taste like?
Add tonic water ice cubes into the mix, and it opens up even more play possibilities. Can you see a difference between the two types of ice cubes? Can you feel a difference? Can you taste a difference? What does tonic water ice taste like? Do you like it? What do you think makes it glow?
The kids wanted to break the ice cubes apart, so I let them have a go with their (real, but small) hammer. My kids play with real tools quite a bit, but I’ll let you judge whether this would be appropriate in your house.
(As one of my lovely readers Debbie pointed out, you might want to put on safety googles on your kids first, in case the ice shatters and little pieces fly up into their eyes. Good point, I should have thought of that. We have these ones, which my kids usually love to wear.)
And then they tasted. They decided that the water ice cubes were delicious! The tonic ones they weren’t such a fan of, although they did go back for third, fourth and fifth tastes, just to make sure.
Because sensory play like this is so open-ended, you could tailor this activity to suit any age group.
Toddlers will love playing with and tasting the ice (although you’d probably want to be in charge of the black light).
My preschooler is really fascinated with the cause and effect of UV light play at the moment. She loves to hold the UV torch. (Embarrassingly she also loves to march around our house showing any visitors our ‘invisible’ stains. Eek!)
Whereas my 5.5 year old loves to use sensory play like this as a brain break from the intensity of school. She adds a few of her figurines, and gets swept up in imaginative play.
It doesn’t matter if kids don’t understand all the theory behind it at this point: it’s enough that they can see it, and touch it, and be amazed. They are learning to associate science with fun and wonder. Using words like temperature, absorb, transparent, fluorescent, ingredient, quinine and ultraviolet light in context increases their familiarity with these words. I’ve found our kids quickly grasp the basic meaning (faster than what we suppose), and start to test out using these words themselves in their play.
Low power long wave ultraviolet light (UV-A light), such as is emitted by black lights, is not a hazard and can be viewed without protection. However, as with all torches, please don’t shine directly into eyes.
If your kids are using hammers or mallets to break apart the ice, safety goggles will prevent any loose shards from flying up into their eyes.
All kids’ activities on this blog require attentive adult supervision. Parents and carers will need to judge whether a particular activity is appropriate their child’s age and skill level. Click here for more information.
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