No 17 completed: Start a fire from scratch

I knew there were multiple ways of starting a fire from scratch and although initially intending to rub sticks together, in the end I was persuaded that using a magnifying glass would be quicker. So we set up a piece of wood with some cotton wool attached on a sunny day, in the hope we could set it alight . And to all of our surprise, after a while of holding the magnifying glass at the right angle, the wood itself began to smoke and burn (I saw a flame!).

Picture below as proof: