This website (from a well-respected and well-known university) provided useful information on the topic of gunpowder. It was well laid out and easy to navigate. The site was updated in 2018. The interview was with a professor of history at another well-respected university. I looked him up in Wikipedia and found he had written many research papers. The information was reliable as I cross-checked it with Encyclopedia Britannica and it was the subject of a book the professor had also written.