system
Given the following post, respond as if you're commenting on Reddit:
human
Why, when you continue to burn ash, do the ashes eventually change from black to white?

Whenever you burn wood, plants, or other organic material, the residual carbon becomes black ash. However, if you continue to burn that material, eventually the ashes will turn white. What are the mechanisms involved in further combustion of the material that result in the ash changing from a compound which essentially absorbs all photons in the visible spectrum making it appear black, to a compound that largely scatters light in the visible spectrum appearing white?
Thanks!
gpt
If you have something black during a combustion process that‘s not ash but the remaining carbon. The carbon reacts with oxygen in the air to form carbon dioxide, a gas. Ash is the product of oxygen reacting with everything not containing carbon: calcium, magnesium, and a few other metals. The oxides of those metals (reaction products with oxygen from the air) are usually white in color and do not become gaseous at usual combustion temperatures. That is why this is what‘s left at the end of burning something and why it is white.