OK, not trying to be funny or anything but what about using a condom rather than a plastic baggie? I've never actually tried it but I've thought about using them in ground based fireballs to contain flammable liquids rather than baggies....just a thought
Recently I bought a couple of Kg of KNO3 from GD, it was a really off white colour and gave much more of a red than lilac flame colour than KNO3 I have bought from them before. Might be the same stuff.........