system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does metal change different colors when it's heated and allowed to cool?
gpt
if you are talking about heating metal up to like 1500 C or more, it turns metal > brownish > reddish > white and back the same way because of something known as blackbody radiation.


basically everything, coloured or not, transparent or not, will go through the same colour changes as it is heated, and begin to give off light at certain colours at certain temperatures. Basically brown (really just dull red) going to red / orange then white. Which is where 'glowing from the heat' comes from.


if you're talking about certain metals (say, iron) turning bluish at times, it's because of the thickness of iron oxide (or any other metal oxide) forming at very precise thicknesses, causing something known as thin-film diffraction.

Pre-requisite: you know that light is made of different colours, which means different wavelengths - wavelengths literally is a measure of distance. very small ones when we're talking about colours that we can see.

back to metal: as iron (or other metals) are heated, they form the corresponding metal oxide (the metal is being burned!) and the thickness of the layer that grows on the surface, will be similar to wavelengths of certain colours, which causes light that shines on the metal to be bent a certain amount, depending on the thickness of the oxide (metal ash!) and when the bent light reaches our eyes, we see it as colour.


Disclaimer: There's alot more science left out.