Wood ash isn't carbon. It's mostly remnant minerals like sodium, potassium, and calcium after the carbon has burned away (hence "potash" = "pot ash" as potassiu

Wood ash isn't carbon. It's mostly remnant minerals like sodium, potassium, and calcium after the carbon has burned away (hence "potash" = "pot ash" as potassium's namesake). The proper comparison here would be charcoal. (Volcanic ash, on the other hand, contains common rock-forming elements: silicon, magnesium, and iron, with the proportions depending on the type of volcano.)