If I super heat a metal and it turns visibly red what is happening? Was it already emitting infrared and as it gets hotter the frequency shifts up? Or is it still emitting infrared but has a wider band of frequencies it is emitting as well (i.e. is it emitting frequencies below infrared as well as visible red)?
Yes, as you heat something up to “red hot”, the glow shifts from infrared to being partly in visible red frequencies. This is why a blacksmith can use the color of a piece of hot iron to tell how hot it is.
(This isn’t the only way hot things make light, though — for instance, flames can glow with odd colors like green or blue due to specific chemicals burning.)
If I super heat a metal and it turns visibly red what is happening? Was it already emitting infrared and as it gets hotter the frequency shifts up? Or is it still emitting infrared but has a wider band of frequencies it is emitting as well (i.e. is it emitting frequencies below infrared as well as visible red)?
Yes, as you heat something up to “red hot”, the glow shifts from infrared to being partly in visible red frequencies. This is why a blacksmith can use the color of a piece of hot iron to tell how hot it is.
https://en.wikipedia.org/wiki/Black-body_radiation
(This isn’t the only way hot things make light, though — for instance, flames can glow with odd colors like green or blue due to specific chemicals burning.)