To Alan: I know it can be done safely, and I know you can do it, but people seem to post about it with no clue about safe procedures. Liquid propane expands nearly 300 times it's volume into the gas. If people post about filling bottles they should at least give some clue on the safe procedures or 100's of people with even less knowledge will read it. It only takes 1 out of those 100's to get it wrong. I checked on the figures and there are 600 propane bottle explosions a year in the US, mainly caused by people overfilling bottles. Less dangerous than driving, but still something to be aware of.
It's like making flash paper as used in magic effects. It can be done by mixing two acids in the right proportions and soaking tissue paper but so many people have got their hands blown off trying it and getting it wrong, it's hardly worth doing.
To Richard: There is also the danger of an overfilled bottle, just exploding due to temp change or physical shock though I believe that is pretty rare.