Forced Patina on Carbon Steel Knives
Carbon Steel knives are great for getting that razor sharp edge but they do require some regular maintenance to avoid rusting. There are a few ways to help protect your carbon steel knives however. You can simply keep them oiled. Some oils used are Danish Oil, Tung Oil, or even olive oil are all great food safe oils or if your not going to use your knife for food and game prep there are a lot of other oils out there to use. Another great way to avoid the corrosion of your knife is to force patina on it. I know it sounds counterproductive but it actually works and can reduce the maintenance of your blade dramatically.
The process of forcing patina is fairly easy and can be done a couple different ways. The idea is to use an acid to speed the natural patina process along. So you will need to wipe your blade clean using alcohol or acetone. These are solvents that will remove any grease or oil on the blade that will interfere with the patina process. I prefer to use denatured alcohol or isopropyl with either a cotton ball or small cotton rag. Once the blade is clean you are ready to begin.
You can quickly and easily create an even patina layer over the entire blade simply by pouring vinegar in a glass tall enough to submerge the entire blade. I normally cut the top off of a water bottle and this will allow you to submerge a small to medium blade. Let the blade soak for one hour. It will bubble while the reaction is taking place. After one hour you can simply rinse the blade in cold water and use a piece of steel wool to scrub it clean. This will keep the patina even as well. If you want to add a design I suggest using the vinegar soak first so you will have a patina over the entire blade and then use mustard to make designs or even words on your blade. I’ve seen a number of articles as well as videos on youtube where people will simply use fingernail polish to draw or write on the blade prior to soaking in vinegar. This will work but the problem is the area covered with the nail polish will not have a protective patina layer on it. This is why I think my method is much better.
After you clean your blade again with alcohol and pour some mustard out in a small cup and use a small paintbrush or Q-tips to apply to the blade. I like to take the Q-tip and cut it in half so I can use the stem to draw fine detailed lines. Keep a rag near to wipe the excess off the tip and everywhere you remove the mustard from the blade will create dark patina at the edges of the mustard. Once you have your design let it sit for one hour and then again just wash off in cold water. For this I actually added 1 gram of powdered acid blend (a mix of Citric, Malic, and Tartaric acid found in most beer/wine brew stores). Not sure if it actually made much difference but it did seem to make darker lines. The PH of plain mustard is about 3.6 and the blended mustard I made was 2.7 so this should speed the process along slightly more.
Pretty cool huh? If you want to change the design you still can. Just buff this off with steel wool and then soak in vinegar again. Then buff again with the steel wool and the design should be fairly faded.
To completely remove you can use a rubberized abrasive block that will remove the patina much better. Then simply start the process over as one of these blocks will scrub all of the patina off. After soaking in vinegar again and wiping clean use mustard again to create your new design. Then let it sit for another hour and wash off with cold water. Once you have the design you want add a light coat of olive oil over it to protect it while in storage. Anytime you use your knife always clean and oil it before putting it up and it will keep this patina for a long time. Now you can enjoy your own custom blade.