How Can I Stop My Carbon Steel Knife From Rusting?

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Carbon steel knives can be a beautiful pain in the ass sometimes. They are usually sharper, a dream to sharpen, and have amazing edge retention. Unfortunately, they can rust if not given a little extra care.

After a while the steel will oxidize and react with the air and start to change colour. Your knife will take on hues of grey, blue and black; this is a good thing. It means that a patina is on the way. Think of a patina as a little extra help in the war on rust.

Adam, who works in our Edmonton Knifewear, has figured out a pretty easy way to force an early patina onto a carbon steel.

What you’ll need: 

• Cheap, pre-ground instant coffee (Folgers, Nescafe, Cheap cheap store brands). The cheaper the better, think of the coffee you'd get at 3:30 AM in a Gas Station. 
• A means to brew the awful coffee.
• A tall and slender vessel, like a flower vase. Double stacked XL To-Go Coffee cups work as well.
• Your carbon steel knife
• A small sponge/dish cloth

Step 1: Brew that coffee!

Brew a STRONG pot of coffee, so strong that you’d be jittery for days! Now chill it. You want the coffee to be cold for this process, we aren’t making a knife & coffee soup.

Step 2: Find a vessel for your knife

• Using your skinny & tall vessel, place the small sponge or dish cloth in the bottom. Put your knife in gently, tip down. 
• Pour in the chilled coffee until it covers the entire blade of your knife, but does NOT submerge the handle.
• Leave the knife in the solution for 6-8 hours minimum. Overnight is ideal. A full 24hr will create the most striking effect.

Step 3: Emergence

After the recommended amount of time has passed, take the knife out of the coffee and wipe down with a damp cloth and dry thoroughly. Your knife has undergone an incredible transformation and is now a lot easier to maintain. Still wipe that blade down and keep it clean and dry, but it’s going to be a lot more rust resistant than before. 

Step 4: Hone and strop that knife! 

Coffee forced patinas aren’t nearly as acidic as lemon or vinegar patinas, but the acid in the coffee has reduced some of the polish on your cutting edge. Plus, you should always hone and strop before the last (optional) step!

Step 5 (Optional but suggested):

You want to get that coffee smell off the steel, so I recommend cutting up some yellow onions to pull out the coffee fragrance. Then fry those onions.  Coffee fried onions will win you the adoration of all your foodie friends at that next pot luck!

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Pretty cool, huh? This process produces spectacular results on Shirogami #1 or #2.It also does wonders on Kurro-uchi finished knives as well as Aogami steels.  The results are less striking but just as functional.  My Moritaka 210mm Kiritsuke is almost jet black!