A small, primitive village has yet to discover fire, which is a good thing because there are highly flammable (but not otherwise dangerous) gasses in the air. The heroes, blissful in their ignorance, don't know that and think it a wonderful idea to show the locals open flame.
The idea of using tattoos to contain magic powers is not a new one. The Ink gauntlet follows the basic premise of using rare and precious inks to inscribe spells into the skin of a mage or would be spell-imbued person. Some of these inked spells might be permanent, while others might fade after being used once, or a preset number of times.