About patina
Hi there!
I'm Tomo, the newest member of KATABA. I'm still learning about Japanese knives, and I’m really looking forward to meeting many of our wonderful customers!
Today, I’d like to share something I recently learned — it’s about patina.
When metal oxidizes, it can rust. But patina is a thin oxidized layer that forms on the surface of the metal, especially on carbon steel knives. This layer actually helps protect the knife from further oxidation, meaning the inner metal is less likely to rust even when exposed to air.
A good example is kurouchi — the black finish often seen on traditional knives. This is a form of black oxide coating that helps prevent rust from progressing.
In the photo above, the top knife is brand new, and the one below it is the same type but well-used.
The darkened core area on the lower knife is a sign that a stable patina has formed — specifically, a black oxide film. This is a good, protective state.
Here, you can see a patina that's right on the edge of turning into rust.
Some people actually love this look — it gives a knife a cool, vintage vibe and a sense of character. But if you leave the patina untouched for too long, it can become difficult to remove and eventually turn into rust.
So, we recommend cleaning off this kind of borderline patina regularly.
How can you prevent this kind of unstable patina from forming?
If the blade is dirty, moisture in the air can react with it and create an acidic surface, which speeds up oxidation. That’s why it’s important to:
- Keep the blade clean
- Wipe off any moisture thoroughly
- Store it in a dry, well-ventilated place
Another effective method is applying a light coat of camellia oil to prevent the blade from being exposed to air.
Here, you can see rust just starting to form on the surface.
In this case, it’s best to remove it as soon as possible!
After rust removal, the blade looks beautiful again, right?
It can be tricky to tell the difference between patina and rust, but don’t worry — we sell rust-removal products and are happy to help if you have any questions!
Thank you! Have a great weekend!