I still had some charcoal hand soap I had bought at the Shaanxi Dr. CitySuper. I took this (potato quality) picture before the character washed away. 炭 (tàn) means “carbon” as in “coal”.
山 (shān) means “mountain.” 灰 (huī, meaning “ash”) is composed of 火 (huǒ, meaning “fire”) with a “hand” radical, as in “what’s left after the fire which can be held in your hand.” So 炭 (tàn) literally means “ash under the mountain.”