Coloured crème brûlée

Do you know what happens when you add salt to flames? Those flames turn a super cool colour!

OK, here's the trick: Salts are actually made of two types of particles, metal particles and non-metal particles. And it is the metal particles that provide the special colours (such as sodium, strontium, copper, and so on).

Let's look inside such a metal particle. In the centre are even smaller positive and neutral particles, while the negative particles orbit around them. When you heat the salt, some of those negative particles (electrons) jump to a higher orbit. But they cannot stay there for long, so they quickly jump back to their old spot. And when they do, energy in the form of light is released!

And here comes the funny part: that light has a special colour, depending on the type of metal in the salt. If the light has a wavelength we can see with our eyes, we get a coloured flame! For example, copper makes a blue-green flame, strontium makes red, and sodium makes yellow.

Fireworks also owe their beautiful colours to the various metal salts that cause certain colours when heated.