These miners extract sulfuric rock—formed after the blue flames have gone out and the sulfur gas has cooled and combined with the lava to form solidified rock—for use in the food and chemical industries. "To double their meager income, the hardiest of these men work nights, by the electric blue light of the sulfuric acid exhaled by the volcano," Grunewald says. Some of the workers are children, seeking to support their families by any means possible.