Putting it in a clear plastic baggie magically makes it safe:

Mind you, I had packed the stuff safely. It was in three separate jars: one of charcoal, one of sulphur, and one of saltpetre (potassium nitrate). Each jar was labeled: Charcoal, Sulphur, Saltpetre. I had also thoroughly wet down each powder with tap water. No ignition was possible. As a good citizen, I had packed the resulting pastes into a quart-sized “3-1-1” plastic bag, along with my shampoo and hand cream. This bag I took out of my messenger bag and put on top of my bin of belongings, turned so that the labels were easy for the TSA inspector to read.