How is iron black, yet steel light grey?
In: Chemistry
Grey cast iron is almost black on the outside because of the slag (surface impurities) that cling when they are cast. When you machine it, it is a dark grey.
There is also white cast iron, where iron and carbon form iron carbides, which give is a whitish colour.
Steel can be dark grey to silvery, depending on what is alloyed into it. High Speed Steel is silvery when surface machined, but when it breaks (it is quite brittle) it is also dark grey.
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