Don't panic when your high-carbon blade changes color. It is supposed to. You just need to learn the difference between character and pure neglect.
This carbon steel blade shows the three realities of reactive steel. A new blade often starts out bright and shiny. That grey, blueish discoloration next to it is patina – a natural surface change that can offer some resistance to further reaction, though it is not rust-proof. That orangy crust at the tip, however, is rust. Your blade is telling you that you've left it wet for too long.
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Patina is part of the story. Carbon steel reacts with moisture, acids, and foods. Over time, this can create grey, blue, or dark discoloration called patina. It changes the blade's appearance and can reduce how readily the surface reacts, although it doesn't make the steel rust-proof.
Rust is different: look for orange-brown spots or a rough, flaky surface. If you spot early rust, clean and dry the blade promptly, using an appropriate treatment for its finish. After cutting acidic ingredients, give carbon steel a quick rinse and wipe rather than leaving it covered in food residue.
