A flame that burns with heat, but no light. There are several ways to start darkfire, including friction in specific woods grown in the land of Umbra, but the easiest way is generally with a drop of blood from someone either of the Darkness or of the Kin with Darkness in their blood. The chemical qualities of that blood can, with certain incantations, alter the makeup of flammable goods, allowing it to catch with darkfire instead of ordinary flame.
This particular conflagration is especially useful when traveling at night. While it does not give off as much heat (most would say a “different” heat), it is sufficient to keep travelers warm, to cook meat, and to avoid detection. The flames are generally a deep indigo in color, rendering them nearly invisible at night.
Friction and specific woods grown in the land of Umbra are required to begin it; a drop of blood from many members of the Darkness (or Kin) can also cause this dark combustion in ordinary flammable goods.