When it comes to modern production swords that we use often for cutting practice, proper and frequent maintenance is necessary to keep them in good condition. With common targets such as soaked tatami mats, water-filled plastic bottles and soaked rolled newspaper, we need to make sure that all water, residue and debris is cleaned from the blade’s surface and that the blade is then thoroughly dried and coated with a thin layer of protective oil to prevent rust and corrosion. Periodically, we also need to clean and re-oil our blades that might not see regular action.
Traditionally this maintenance was done with choji oil, uchiko powder, and rice paper. While these items can still be used, I prefer modern household products. I DO NOT recommend using the following products or methods on antique blades but they should be sufficient for most modern steel and affordable working blades. Most cheap cleaning kits you can buy anywhere will come with choji or camellia oil, a powder ball with low grade uchiko(which can actually be damaging), and some rice paper or cloth.
This is what I use for my modern production sword blades and carbon steel knives and tools.
I use a standard cleaning solution with ammonia such as Windex or Glass Plus to get the residue and debris and old oil off of the blade surface.
Paper towels or clean cloth
I feel paper towels are just fine for the average modern steel. If you are worried about the build up of micro scratches over time, you might want to use only soft cotton cloth or micro-fiber on your blades. I do use a cotton flannel cloth for applying new oil.
If there is some really stubborn residue left on your blade after using the above cleaners, you can use something like quality uchiko powder or talcum powder. They are mild but can still cause micro scratches. If you use your sword to cut with often, you will have much worse scratches to begin with.
Most of the time when cleaning blades that haven’t been soaked with water to the point where it runs down the length and under the habaki, it is not necessary to disassemble the sword before cleaning. For this demonstration, I will remove the tsuka and fittings.
Remove the mekugi (bamboo retaining pin/pins)
Most of the modern full size katana will have two mekugi but some might only have one. Remove them carefully with a mekuginuki (small brass hammer) or similar tools.
Remove the tsuka and fittings, including the habaki
Sometimes it might be difficult to remove the tsuka even when the mekugi have been removed. To help loosen the tsuka you can use a small wooden block and a rubber or rawhide mallet. I place a thin piece of leather between the seppa and habaki and the wooden block to protect the fittings. Lightly tap the top of the block a few times until the fittings and tsuka become loose enough to remove by hand.
Wipe down the entire length of the blade
During this step you must be 100 percent focused on what you’re doing, one slip of concentration can lead to a serious cut. Start at the base of the blade, under the habaki but not on the nakago, it’s good to build up a patina on that portion. Apply the paper towel or cloth with light pressure and wipe both sides of the blade from the base to the tip moving in one direction only and with the sharp edge facing out.
Once the blade is clean of dirt and grease, you can give it another pass with some rubbing alcohol. Make sure the blade is then fully dried off. Please stay focused during this step as well. You should obviously also stay focused on what you’re doing during any activity where a sharp blade or tool is being used.
Apply new oil
I find the easiest way to do this is to use a piece of soft cotton/flannel cloth that is saturated, but not soaking with clean oil. I use the same cloth over and over again and only occasionally need to add more oil to it. You can do this as long as you keep the cloth clean of dust and dirt.
Very lightly, wipe the blade with the oiled cloth from base to tip evenly applying a super thin coat. Once done, you shouldn’t even really be able to see the oil. If it beads or pools, you’ve added too much.
I store my oiled cloth in a small plastic box to make sure it stays clean until the next use.
That’s it. Just do this as often as necessary and always after target practice or if the blade has been handled with your fingers.