Hi @edouard, thank you so much for watching my vid and I am very happy knowing that it also made you happy.
When using fluid paints you often get air-bubbles in the paint that can cause tiny holes when it dries so I will run a torch-flame over the paint to bring the bubbles up to the surface. This can also create new colour cells in the paint.
So the black lighter is the one I use to do this but the button is broken so I have to use the red lighter to light the black lighter.
Sorry I hope that all made sense - however, I hope to make more videos showing the whole process.