A few years back an old black powder shooter was telling me that there was a shortage of flints at one time. He said that many shooters tried, with success, using broken pieces of Corning Wear cookwear. Those of you that are "pc" in your thinking have forgotten your history. Fint and more so pyrite was a controlled commodity in years gone by. Flintlock shooters have used other materials to get a spark. Jasper, chert, quartz, obsidian, and yes broken pieces of ceramic.