So, you got a new custom knife, inherited an heirloom knife, or simply noticed some rust or tarnishing on a piece you’ve had for a while. Here are a few tips and ideas that may help you better take care of your cutlery, whether that is kitchenware, hunting or EDC gear, and many older pocket knives were made of carbon steel and not stainless steel.
First, if you have let a knife or tool rust you are not a bad person. This is the nature of steel and iron. It will rust and patina. Oxygen, moisture (including humidity), hand oils, food acids, and countless other unavoidable elements in nature are conspiring against the finish of steels. This is why we paint cars, blue or treat weapon barrels, powder coat, etc. However, with proper care, a carbon steel knife or tool can last multiple lifetimes. Below are a couple things I do and suggest to prolong the life and appearance of your knife.
1. Keep it clean and dry. This is paramount. Ensuring you clean and dry your knife after each use will significantly increase its life. Be reasonable with this though. There is no need to break out soap and water every single time you pull out your knife, and there is never a time to put a carbon steel knife (or any knife that is not stainless steel) in the dishwasher. Often, simply wiping it down carefully with a cloth will suffice. However, if you cut food, meat, or get the knife dirty I suggest cleaning it prior to storage. Several sources instruct to wipe the blade off every few cuts with acidic, bloody, or citrus foods.
2. Use a blade wax or oil. Even while your knife is not being used, the elements are trying to break it down. A coat of blade wax (there are food safe varieties for kitchen tools) or oil will help keep moisture from attacking the steel. Any oil would work, but they make knife oils or gun oils. Also, for kitchen knives, mineral oil works well when not using wax and any oil you don’t mind eating would suffice.
At this point, it would be good to touch on “patina,” its cause and essential function with a carbon steel knife. Patina is, basically, an iron oxide (rust) that with stain the steel, but without the flaky, bubbly aspect of rust. As you use a carbon steel knife, it will develop this patina naturally. This helps protect the knife from additional rust and will shield the knife. However, the knife should still be cared for. Some folks don’t like the look of patinas, and I would recommend stainless steel for them. Carbon steels will hold an edge longer, but there are the downsides as well.
If you do happen to notice some rust spots on a knife or unwanted patina, often times, some fine (00-0000) steel wool is useful to scrub this off. Make sure to oil or wax after this. Note: This may remove some of the "black" oxides on Damascus blades, reducing the contrast.
That’s really it regarding maintenance of a carbon steel knife. Keep your knife clean and oiled or waxed and it should last longer than you.