Coal extender is virtually any material that is fine textured and flammable enough to add directly to a coal or ember in order to make it larger and keep it going longer. Coal extender can be added to a coal while it’s still in the notch when you’ve made a bow drill ember. Or it can be added to the core of a tinder bundle when you’re using flint and steel or a magnifying glass to kindle a blaze. You can add it to an existing ember, or place it where an ember will go. Many good coal extenders are already a fine fiber, and the rest should be easily turned into dust, fiber, or powder. You can grind coal extender material between two rough stones as if you were milling flour. Scraping can also work, and it can be done with a sharp stone or metal blade. Filing or sawing can make a great powder. Some coal extenders can even be crumbled into dust bare handed. And all coal extenders should be as dry as possible when being used.