system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: What’s the stuff that falls off the hot metal in metal forging?

It’s super satisfying watching metal get shaped into whatever it’s going to end up being but there’s always like thin layers of metal breaking off the second it gets crushed again ? I’ve always wondered this hmm.
gpt
That's called scale.  Its an oxide, and basically a layer of rust from the heat. It doesn't "look rusty", but it indeed is a layer of iron oxide.   Every time you heat the metal, you loose some metal to oxidation because of the composition. Its mostly iron with some carbon and other things.  Forging temperatures require oxidizing flames (as in forced air) of sorts to make the flames hot enough to make metal malleable, and those oxidizing flames oxidize the metals themselves.