Quote from : The Fifth Elephant Book

Vimes, listening with his mouth open, wondered why the hell it was that dwarfs believed that they had no religion and no priests. Being a dwarf was a religion. People went into the dark for the good of the clan, and heard things, and were changed, and came back to tell… And then, fifty years ago, a dwarf tinkering in Ankh-Morpork had found that if you put a simple fine mesh over your lantern flame it'd burn blue in the presence of the gas but wouldn't explode. It was a discovery of immense value to the good of dwarfkind and, as so often happens with such discoveries, almost immediately led to a war. "And afterwards there were two kinds of dwarf," said Cheery sadly. "There's the Copperheads, who all use the lamp and the patent gas exploder, and the Schmaltzbergers, who stick to the old ways. Of course we're all dwarfs," she said, "but relations are strained.