Rust and patina11/3/2023 I'm guessing if we looked closely, we'd see small exposed areas where no passive layer protects against the air, and we'd see rust in those patches.Ĩ: Although there's no surface level rust, the deep pitting above the polished bevel looks concerning. Noticed how the passive layer on top doesn't have the same discoloration. Again, there are some darker spots that I'd be concerned about for pitting corrosion, but given the surface condition of the blade, it seems likely that these spots are remainders of already cleaned-up rust.ħ: Rust bucket! This is what happens when rust is allowed to spread. This black/gray discoloration is very common on older knives. Again, this can be confirmed by seeing whether the rust flakes off into a towel or fingernail.!<Ħ: Patina. This one is easy to see because you can spot the spreading pattern - dark reddish-brown at the center that gets lighter spreading away from the epicenter. If there's any flaking, it's rust.ĥ:>! Definitely rust. It looks ugly, but you can confirm it's not rust by wiping a towel or rubbing your fingernail over it to see if the orange/brown color flakes off. Pitting is the most insidious kind of rust since it can hide for so long, destroying the structural integrity before it's visible.ģ: Likely brown patina, I typically see this after chopping cold onions. Blues and yellows are a classic patina and considered very beautiful.Ģ: Most of the brown looks like surface-level patina, but the dots have me worried about pitting corrosion. Nine images of knives with discoloration denoting either rust or patinaįeel free to click on the spoiler tags below to compare answers once you've had a chance to think it over:ġ: Patina. Can you tell which of these images is showing rust and which is merely patina? This being said, it can sometimes be quite difficult to tell the difference and so the graphic below is presented for your consideration. Obviously there's a lot of chemistry involved that is being oversimplified above, but the main difference that matters is rust is always destructive while patina is not. In the knife world, patina specifically refers to a chemical stabilization of the surface such that ferric oxide reactions become "passive," slowing or halting entirely.
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