rusty carbon steel ?
Are you scared to buy a Carbon Steel Knife, because you think it’s going get all rusty and gross.
The reality is you won't believe how easy it is to care for a carbon steel knife and actually how that aged grey appearance will make it perform better than stainless steel.
First, why does carbon steel rust?
Carbon steel is traditionally the steel used to make knives and cutlery with stainless only being developed in the 20th century. It’s a combination of iron and a small percentage of carbon which allows it to harden sufficiently to keep a sharp edge. Iron reacts with oxygen and water to form rust known as iron oxide or Fe203.
Ok so, we know that iron reacts with oxygen and water therefore removing one of these elements will prevent rust - right ! - well yes and no. The bad news is rust will appear regardless of what you do and in fact we need rust on a carbon steel knife but just in a different form.
What we need is Patina or Magnetite Fe304 as it is known chemically. It's essentially heated rust ( not a chemist BTW) and it’s the type of oxidation that helps protect a carbon steel knife from the dirty rust ( Fe203).
Ok so, how do you get one and not the other. ?
Dirty rust appears when a knife is wet and left wet for a period of time and oxidation occurs. Therefore to prevent dirty rust. Keep your knife dry. After use, clean the blade with hot water and dry thoroughly, no need to dunk it in the sink with all the dishes, just a light wash and good dry. A new knife can benefit from a wipe down with olive or veg oil after use as well until the patina is developed.
To develop Patina - there are 2 ways.
Forced Patina - coat the blade in a food acid and let science do it’s thing, it’s not an exact science by the way and may take a few goes to get enough of a coating. Anything from mustard to apple cider vinegar will work ( not white vinegar ). Alternatively you can chop up a bunch of onions and tomatoes - like a lot of them.
Time - patina will develop naturally over time with normal use and care ( keeping dry ).
What if my Knife is already rusty ? - well that's unfortunate, but luckily there's hope.
You can convert dirty rust into magnetite ( patina) by immersing the blade ( blade only ) in boiling water for 15 - 20 minutes , then scrub with dish soap and steel wool or scotch brite. This process will convert the rust to magnetite (patina)
Or if you have 1200 grit wet/dry sandpaper you can sand the blade and lubricate with glass cleaner ( with ammonia). Make sure you wash with dish soap and dry after - this will remove rust but also take the blade back to a shiny steel look - it’s a good place to start if you have an old neglected knife that you want to restore. Then just let time do it’s thing with the patina.
Why is Patina Good ?
Magnetite not only protects from rust and wont come off into food, it also aids in food release from the knife - that is, food sticks less to patina than shiny or stainless steel- I get that it may not be a huge deal if your just cooking at home , but if your in a busy kitchen doing a lot of food prep, the less sticking the better.
So to recap,
Light wash in hot water and dry - oil if you want ( I live in a humid environment, so oil definitely helps )
Let Patina develop - Forced or naturally - Most of the carbon steel knives I make have a forced patina.
Remove dirty Rust - heat blade in boiling water, scrub and dry.
Enjoy and wear your patina with pride.
PS. - There’s always a lot of discussion about how to store knives, some say never use a knife block, other’s say never put them in a cutlery drawer or only use a magnetic rack. Well, I can only tell you from my experience with knife storage which I wrote about here.
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