The invisible beaker is a classic science activity and a fantastic example of “science magic” that’s sure to provide a wow moment to children (and adults) of all ages! It’s inexpensive and very easy. You need a large and a small glass beaker and enough clear cooking oil to cover the small beaker when it’s placed inside the larger one.
The beakers must be made of borosilicate glass, such as Pyrex, or the demonstration won’t work. The secret to the small beaker disappearing is because of something called the Refractive index.
Invisible Beaker Demonstration
You’ll need
A large glass beaker
A smaller glass beaker
Clear cooking oil, such as vegetable oil
Sharpie – optional
Instructions
- Carefully place the small beaker inside the larger beaker. You should be able to see both clearly.
- Pour the oil into the smaller beaker until it overflows and completely covers it, making the small beaker appear to disappear.
Optional challenge – draw a picture on the smaller beaker and watch as it seems to float inside the big beaker.
Why does the beaker disappear?
Usually, when light travels from one material to another, it changes speed and bends. It is the bending of light which allows us to see the edges of a transparent object.
Oil and glass have the same refractive index (approximately 1.47), which means that light passes through them as if they were a single solid substance. Light doesn’t bend as it passes from one to the other, so our eyes cannot detect the small beaker!
You can see the edges of the larger beaker as the refractive index of air is 1.0. Light bends as it passes from the glass to the air, and so the edge of the beaker is visible.
More science magic tricks
Make a jumping bean with kitchen foil and a marble. A jumping bean takes less than five minutes to make and leaps around like it has a life of its own.
Push pencils through a plastic bag filled with water and be amazed when it doesn’t leak!
Use another clever refraction trick to make a coin disappear!
Last Updated on January 13, 2026 by Emma Vanstone
