Having made some nitrocellulose in my adventurous youth, it is most definitely *not* "cotton soaked in nitroglycerin". Nitrocellulose is made by the nitration of cellulose (cotton), just as nitroglycerin is made by the nitration of glycerin. Different chemicals altogether. Nitrocellulose is very flammable, but it's not nearly as unstable and explosive as nitroglycerin...
[Then there was the crazy neighborhood kid who tried making actual nitroglycerine using his big brother's chemistry set, but wound up pouring what was probably a ml or so of nitro down the drain, because he misread the final instructions. Good thing nobody in the street flushed their toilet too hard that day. Ah, the happy boyhood memories of experimenting with dangerous chemicals...]