The Skittle Rainbow
Most people think they know how this experiment works.
Colourful sweets. Water. A rainbow.
Simple.
But then something strange happens.
The colours race across the plate… yet when they meet, they refuse to mix.
Even stranger, with one tiny change, you can make the rainbow appear to move backwards.
Can you work out what’s really going on?
5-12 yrs
Easy
25
min
Stage 1-3
Mission Briefing.
Designed by Darin Carr (BSc, DipEd)
NESA Accredited Teacher Chemistry & Physics Specialist
Creator of the LAB™ Learning System
Professor Picklebottom
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The Skittle Rainbow
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NESA Accredited Teacher
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High school chemistry & physics specialist 30+ years
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The Crazy Scientist in primary schools — 15 years
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International conference presenter on science education
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Creator of the LAB™ Learning System
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Curriculum aligned: NSW Science & Technology K–6 (2024)
A picture is worth a thousand words — check this out and see if you can spot the science hiding in plain sight.
Mission Equipment
One packet of Skittles — you need at least 2 of each colour (red, orange, yellow, green, purple)
A flat white plate with a rim
Room-temperature water
One sugar cube or one teaspoon of loose sugar
Optional: a dropper or spoon for precise water pouring
Optional: M&Ms or Smarties for comparison testing
Let’s Investigate
1
Build the circle
Sort your Skittles by colour. Arrange them in a circle around the rim of the plate — one colour at a time, in rainbow order: red, orange, yellow, green, purple.
Use at least 2 Skittles of each colour
3
Add water
Slowly and carefully pour room-temperature water into the centre of the plate until the base is covered — about 4–5 mm deep.
Try not to disturb the Skittles. Then step back and watch without touching the plate.
5
Predict again
Now look at the coloured streams meeting in the middle.
You are about to place a sugar cube directly into the centre of the plate — inside all the colour streams.
Predict: what will the sugar cube do to the colours around it? Will it pull the colours toward it, push them away, or have no effect?
2
Predictions
Before you add any water — predict. When water touches the Skittles, the colour and sugar coating will dissolve and spread inward across the plate. When the colours from different Skittles reach each other in the middle, what will happen?
4
Observe the boundary
Watch as the colours flow inward and meet.
Look closely at the point where two different colours reach each other.
Describe exactly what you see — do the colours blend, blur, or hold a line?
6
Add the sugar cube
Once the colour streams have met and settled into a stable pattern, place a sugar cube (or a small teaspoon of loose sugar) carefully into the exact centre of the plate.
Watch what happens to the boundary lines.
Did it work? Share the science! Tag @the_crazy_scientist on Instagram — we love seeing your experiments!
The Crazy Scientist LAB Learning System™
Every experiment follows The Crazy Scientist Lab Learning System™ — a simple way to help kids think like real scientists.
We
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LINK to what they already know,
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ACTIVATE curiosity through hands-on discovery
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BUILD understanding that actually sticks.
Have you ever dropped a single drop of food colouring into a glass of still water and watched it slowly spread — without stirring, without being pushed — until eventually the whole glass was coloured?
What is carrying the the colour? Something is moving — but nothing is pushing it. What do you think is driving that movement?
Now look at the Skittles arranged on the plate. Each one has a sugar-and-dye coating that is about to dissolve.
Before you pour a drop of water — predict: will the colours flow toward the centre, away from it, or stay close to their Skittle? And when the colours from different Skittles reach each other in the middle — will they mix, or will they stop?
You've watched a rainbow form — and watched it hold its shape at the boundaries.
Think back to the moment the first colours reached each other. Describe what happened at the boundary. Did they blend, blur, or stop? Was the line sharp or fuzzy?
You predicted whether the colours would mix. Were you right? If the colours stopped at the boundary — think about what was the same about each stream arriving there. What was equal about them?
Every Skittle in the circle dissolved the same coating in the same depth of water at the same time. What does that tell you about the sugar concentration of each coloured stream — and why might two streams of equal concentration stop instead of mixing?
The sugar cube produced a very different result from the Skittles. What was different about how much sugar it added to the centre — and why did the colours respond by moving away instead of staying still?
Solutions flow from where they are concentrated to where they are dilute. When two solutions of equal concentration meet, neither has a reason to flow into the other — and a boundary holds.
"Want the full teacher guide? The Crazy Scientist Lab includes classroom delivery tips, how to manage the WOW moment, differentiation for Stage 2 & 3, — ready to teach tomorrow."
Think Like a Scientist
Scientists don't just do ONE experiment; they change one part of the experiment (independent variable) and then see how it affects another part of the experiment
(dependent variable)
Change ONE variable and test again.
Does water temperature change how quickly the rainbow forms?
Does the number of Skittles per colour group change the result? Compare using 1 Skittle per colour (5 total in the circle), 3 per colour (15 total),
🧪 Try it! Change ONE thing and test again. What did you discover?
Dr Puddledrip’s Science Tip
Want to go deeper? Tap a section below to explore. ▼
The Science Behind It
Why do the colours move?
When water touches the Skittles, something interesting happens.
The colourful coating on the outside begins to dissolve and spread into the water.
Each Skittle releases its own colour, creating the rainbow effect you observed.
But did you notice something strange?
The colours don’t rush across the whole plate. Instead, they seem to travel in organised streams.
Why might that happen?
Why do the colours stop when they meet?
This is the part that surprises most scientists-in-training.
When the coloured streams reach the middle of the plate, they often stop instead of mixing together.
At first glance, that seems impossible.
After all, liquids usually mix when they touch.
So why do these colours sometimes stay separated?
Scientists investigate questions like this by looking closely at what is happening in the water.
Can you think of any ideas that might explain it?
What changed when you added the sugar cube?
The sugar cube created a completely different pattern.
Instead of moving toward the centre, some of the colours appeared to move away from it.
Something in the water changed.
Scientists often discover new ideas when they change just one part of an experiment and carefully observe what happens next.
What do you think the sugar cube changed?
Real-World Connection
Scientists study how substances move and mix in liquids.
These same ideas help scientists investigate:
ocean currents
weather systems
pollution in rivers
how nutrients move through living things
The Skittles rainbow gives us a tiny window into a much bigger scientific world.
Curiosity Spark
The colours seemed to stop when they met.
But what if you used:
hot water?
cold water?
different sweets?
a larger plate?
Would the colours behave the same way?
Or would something completely different happen?
Try next
• See another experiment where the invisible movement of molecules creates a visible effect → [The Pepper Escape]
• Explore how concentration differences drive a completely different kind of colour change → [The Colour Climb]
Extension: G&T Years 5 & 6
Think Like a Scientist
Scientists rarely stop after one test. They change one thing and investigate again.
Try exploring:
1) Hot vs cold water
Does the rainbow form faster in warm water or cold water?
2) Different sweets
Do all coloured sweets create the same rainbow effect?
Challenge Question
Can you find a way to make the colours mix in the middle instead of stopping when they meet?
Record your ideas and test them like a real scientist.
Curious Scientist Question
Many websites say this experiment is caused by diffusion.
But if that’s the complete answer…
Why don’t the colours immediately mix together?
Discover the deeper science inside The Crazy Scientist LAB.
Vocabulary
Know a parent or teacher who'd love this? Send it on! 👇
READY TO TEACH THIS
TOMORROW?
Running the experiment is easy; however, teaching it well is another challenge.
Teachers often ask:
How do I adapt this for Stages 1,2 or 3?
What do I do with fast finishers?
What misconceptions will they have?
How do I structure this for a full class?
What syllabus outcomes does it cover?
What do I say when they ask WHY?
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Every resource is designed using our teaching framework.
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