Fold your paper
For this experiment, you'll need a sunny day, three sheets of paper and a clear, full water bottle with a curved top. The first piece of paper is folded three times down the middle so that it can "create the solid base of embers you'll need when you start blowing it into a flame", says Thompson. This piece should have a black spot to absorb heat when the light shines on it. You can smear dirt on the paper if you don't have a black pen.
Catch the rays
Use the curved top edge of the water bottle as a magnifying glass to concentrate light from the Sun on to the black spot. A good method is to start close and back away until the beam is focused. After that, it should take a few seconds for the paper to smoke. When the smouldering grows to about 25mm, add more layers of paper and swing them back and forth. Flames should eventually burst from the bundle.