Steel blades have to be maintained (greased then wiped) at least every 3 months (though ideally every month) to preserve their polish and avoid rust spots.
Here are some tips for blade care and common issues, to apply only with great caution and care* :
› After cutting, it is normal to find thin scratches on the sides of the blade. They should be easily fixed by using the Uchiko.
› Working on the edge of the blade is a delicate endeavor: try to steady the blade on a metal prop then very delicately going over it with damp 2000 abrasive, with a steady repetitive motion and always in the same direction.
› Cover everything around the guard with adhesive paper so that only the surface you wish to matte remains visible. There exist small metallic brushes that fit onto power drills. A few passes and the mirror-polish stainless steel will take on the desired matte look. To be safe, block the blade in a vice (being careful not to damage it) as it can easily slip out of your hands.
› The tsuba may sometimes get a little loose: this is normal. In most cases it is easily fixed: remove the mekugi (handle pin) from the tsuka (handle) and gently, vertically tamp down the katana on a flat surface (preferable padded with cloth) until every part realigns properly, then re-insert the mekugi.
* may void warranty.
A blade is bronzed by plunging the polished blade into a bath of special salts. It protects against rust, so long as it is not left in contact with anything containing acids, including but not limited to sweat, lemons or even tomatos, vinegar, etc.
A bronzed blade can be sharpened by limiting the removal of steel area to 1mm. The edge will be shiny, but the bronzing will remain on the rest of the knife.
If the knife is properly maintained and oiled now and then, the bronzing will remain intact.