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Shiny egg

By David Shaw, 10 September 2020

Scientists say that soot is superhydrophobic

What happens when you cover an egg in soot? It gets super black, but also super shiny!

Safety: To do this activity, you will need to put your hands near a candle flame. Make sure you have an adult to help.
First aid: If you burn your hand, run it under cold water for 20 minutes. If needed, seek medical advice.

You will need

• Egg
• Water
• Detergent
• Clean tea towel
• Tealight candle
• Matches or lighter
• Glass

What to do

1. Start out by washing the egg carefully with water and detergent. Dry it thoroughly with a tea towel.
2. Light the candle and wait for a minute for the flame to settle down.
3. Meanwhile, put some water into the glass. You will need enough water to cover the egg, but not too much, or the glass will overflow when you put the egg in it!
4. Hold the egg securely, then carefully put part of the egg in the point of the candle flame, keeping your fingers away from the heat. After a second or two, black soot should start building up on the egg where the flame touches it.
5. Slowly move the egg so you can cover more of it with soot. To get full coverage, you will need to adjust your grip on the egg away from the flame, before returning the egg to the candle. You’ll get best results if you take at least two minutes.
6. When you’re happy with the amount of soot, carefully lower the egg into the water in the glass. It will start to look shiny!
7. Remember to blow out the candle when you’re finished!

What’s happening?

Soot is amazing stuff. It’s made of tiny particles of carbon, and it really doesn’t like to stick to water. Scientists say that it’s superhydrophobic, which roughly translates to ‘super scared of water’.

When you put a sooty egg into water, a very thin layer of air is trapped between the soot and the water. It’s light reflecting off that layer of air that makes the egg look shiny. When you take the egg out, it might still be dry!

So how tiny are these particles of soot? Scans show soot particles can be less than a millionth of a centimetre wide. On your egg, there could be trillions and trillions of soot particles, stacked together in complex shapes. This black coating is a carbon nanomaterial!

Real-life science

Scientists are researching soot coatings because they are superhydrophobic and yet cheap and easy to make. Soot layers might one day be used stop ice building up on aircraft wings and power lines, or to stop barnacles and algae from growing on the bottom of ships!

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