On another matter entirely...

[desperance]

If you wanted to sabotage someone's stock of gunpowder, so that it looked and felt and smelled fine but just wouldn't, y'know, explode, how would you go about it? (You can have a couple of days, for whatever you've done to take effect; you can mix in foreign substances or just too much of any given constituent, to unbalance the mix and make it not go bang. Be scientific with me, people. Or imaginative, or both.)

EtA: Dr Gale's Process! It's technically too late for me, but hey. What he can learn in 1865, someone else can have discovered earlier. Powdered glass it is...