Most gunflints were (and still are) made using a blade core technique that's actually been around for many tens of thousands of years. The core is prepared and long narrow blades are stuck from it and then snapped into sections. Other gunflints were made using spalls - very different and something you typically see on French flints - at least in the 18th century. As for wearing a dust mask - don't bother. The only way you'll ever suffer any effects from inhaling the dust (which can lead to a condition called silicosis) is if you're in a confined space working from dusk to dawn for many years. Safety glasses, $#*! yes. Gloves - maybe on the hand you're holding the core with but beyond that - uncomfortable and will ruin any control you might have. Getting cut periodically is all part of the business anyhow.
