A conker that has just burst out of its spiky green case is so shiny it almost looks wet. Put it on the windowsill, though, and look again a few days later. The same conker feels dry, almost like paper, and the shine has gone. So where did the shine go?
What happens when a conker loses its shine?
Conkers are horse chestnut seeds, and their shine is all about light. A shiny surface is so smooth that it works like a mirror: light that hits it bounces back the same way, and you see a small white spot of light. Think of a lake on a perfectly still day, reflecting the mountains. When the wind ripples the surface, the reflection disappears.
Here is the surprise. A conker does not turn dull because its colour fades. It turns dull because its surface gets bumpy.
A fresh conker is full of water. On a dry windowsill that water slowly evaporates through the shell. The conker shrinks a little, and the shell develops tiny folds, far too small to see without a magnifier. Now the light hits countless small slopes pointing in different directions, so it scatters, and the mirror is gone. More outdoor experiments live in the autumn outdoor laboratory.
Try it at home: the shine hunt
Suitable for: 4–12 years
You need three fresh conkers, a small torch or phone light, a box with a lid and a paper towel, a few drops of cooking oil, a plate, and paper and a pencil.
- Shine the torch on each conker in a dim room. Find the small white spot of light and draw it.
- Put two conkers on the plate on the windowsill. Wrap the third in a damp paper towel inside the box.
- Check all three each morning for five days.
- On day five, rub one drop of oil into one of the windowsill conkers, then compare all three.
⚠️ An adult helps with the oil. Conkers must not be eaten, so wash hands afterwards.
The dry conkers lose their bright spot, the damp one stays shiny longer, and the oil brings the shine back at once. So was it age that made it dull? No. It was the surface. Spruce trees fight dry winter air in their own way: why spruce trees keep their needles.
What happens if you rub a dull conker with a drop of water instead of oil, and how long does that shine last?
Questions to wonder about
- Why does a pebble on the beach look shinier after a wave has washed over it?
- Why can you see yourself in a spoon, but not in a sheet of paper?
- A conker is a seed. What do you think the seed needs all that water for?
Every child is made of good atoms
Next time you find a shiny conker, hold it up to the light and look for the little white spot. In a few days it will be gone, and now you know why.
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