system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5 When forging what is the thing falling off the metal and why?

So when I see videos people or machines forging things there is always a part of the outer layer that will fall off after each hit. Pls explain!
gpt
That's called "scale". Most metals, and especially hot metals, like to react with oxygen. So the surface (where it's exposed to the air) forms a layer of metal oxides. Most metal oxides are solid and brittle even at very high temperatures, so they form "scales" that falls off as soon as you distort the underlying soft metal...like when you hit it.