Fire hardening, also known as "fire-polishing", is the process of removing moisture from wood, changing its structure and material properties, by slowly and lightly charring it over a fire. This makes a point, like that of a spear, or an edge, like that of a knife, more durable.
Pre-historic weaponmakers would rub the end of a selected wood pole against a smooth rock surface until a point was achieved. Then the point was heated in a fire, making sure to thrust the point into the coals. This put a light coating of carbon on the surface, which was then polished with a special stone, which ground fine particles of stone into the pitch which had been brought to the surface of the wood by the fire. Subsequent firings and polishings of the wooden tip of the spear would eventually form a hardened glaze consisting of pitch, wood particles and carbon on the tip which could eventually be even harder than a copper tip. This kind of technology was developed by primitive humans at least 400,000 years ago—long before flint or stone points.