Ab Sword · Japanese Sword Care · How to Sharpen a Katana
Every katana edge eventually dulls. Chips happen. Rolled edges happen. The question is what to do about it. Professional polishing — togi (研ぎ) — takes years to learn and costs hundreds or thousands of dollars. This guide covers what you can do at home with a set of whetstones and some patience.
the edge geometry
A katana edge is ground at roughly 10 to 15 degrees per side. That’s measured from the centerline. The total included angle is 20 to 30 degrees. Western kitchen knives run 15 to 20 degrees per side. The katana angle is shallower. Shallow angles slice better. They’re also more fragile.
The kissaki (切先) — the tip — has its own geometry. The boshi (帽子) is the tempered edge pattern at the kissaki. It’s ground differently from the main edge. The shinogi (鎬) is the ridge line running the length of the blade. When you sharpen, you stay below the shinogi. Grind into it and you change the blade geometry permanently.
Traditional Japanese swords are differentially hardened. The edge is hard — around 60 HRC. The spine is softer — around 40 HRC. The edge holds sharpness. The spine absorbs shock. That’s the point of differential hardening. When you sharpen, you work only the hard edge steel.
the stones
The Japanese word for sharpening stone is toishi (砥石). You don’t need the full set a professional togishi uses. A progression of three to five stones is enough for home maintenance.
Start with the blade condition. Chips or serious dullness need a coarse stone — 400 to 600 grit. Touch-ups can start at 1000 grit. The typical progression: 1000 grit to establish the edge, 3000 to 5000 grit to refine it, 8000 grit or higher for the final polish. Some people go to 10,000 or 12,000. That’s optional. A blade at 8000 grit cuts paper cleanly.
Water stones are standard. Soak 5 to 10 minutes before use. The water carries away swarf — the metal particles from sharpening. Oil stones exist but are less common for Japanese swords. Once you use oil on a stone, you can’t switch back to water.
A nagura stone dresses the main stones. A leather strop with polishing compound finishes the edge. Chromium oxide works. So do other fine abrasives. You need a flat surface to work on. A wobbly table gives uneven results.
the angle
This is where people fail. The angle has to be consistent. Rock the blade during a stroke and you create a convex edge. It looks sharp but doesn’t cut well. Change angles between sessions and you gradually change the geometry.
Here’s a way to find the angle. Lay the blade flat on the stone. The spine touches the surface. Slide two or three coins under the spine. That raises the blade to roughly 10 to 12 degrees. Some blades are steeper — up to 15 degrees. Start at 10 to 12 and adjust if needed.
Holding the angle is harder than finding it. The blade is long. The stroke is long. Your wrist wants to move. Use a marker on the edge before starting. Make a pass on the stone. The marker wears off where you make contact. Even wear means consistent angle. Wear at tip or heel means you’re tilting.
the process
Start with your coarsest stone if the blade needs it. Place the blade on the stone with the edge facing away from you. Spine raised to your target angle. Push forward in a smooth arc following the curve. Don’t scrub back and forth. Lift, reposition, make another pass.
A katana blade is 70 to 75 centimeters. Work in sections. Base near the habaki. Middle section. Kissaki. You can work sections separately or try continuous strokes. Continuous looks better but is harder to control. Sections are more forgiving.
After 10 to 15 passes on one side, flip the blade. Do the same on the other side. Feel for a burr — a tiny wire of metal on the opposite side of the edge you’re sharpening. A consistent burr along the full length means that side is done. Move to the next grit.
Don’t skip grits. Each stone removes scratches from the previous one. Jump from 400 to 8000 and the fine stone can’t remove those deep scratches efficiently. You get an edge that looks polished but has weak spots. The full progression matters.
finishing
After your finest stone, strop the blade. Leather with polishing compound. Run the blade spine-first along the strop. Opposite direction from sharpening. Light pressure. About 20 passes per side.
Test the edge. Hold a sheet of printer paper by one corner. Slice down through it. A sharp katana cuts cleanly with no resistance. Tearing or catching means go back to the refining stone.
Tatami mats are the traditional test target. A properly sharpened katana slices through a rolled tatami mat in one cut. Clean, no tearing. Hard targets like bottles damage edges faster. That’s physics.
between sharpenings
Stropping every few uses keeps the edge aligned. Wipe the blade with a clean cloth after every use. Removes moisture and debris. Oil the blade — choji oil is traditional, any light mineral oil works. Prevents rust and oxidation.
Store in the saya (鞘). Make sure the saya is dry. Moisture trapped in the saya rusts blades faster than leaving them out. Humid climates require regular checks even on stored blades.
limits
Some blades need professional work. Chips deeper than a millimeter. Edges badly ground by previous sharpening. Convex, uneven, or reprofiled edges. Fixing those requires removing a lot of steel. That’s risky at home.
Blades with visible hamon (刃文) are differentially hardened. Edge hard, spine soft. Aggressive grinding ruins that heat treatment. Not confident? Stop. A professional togishi has the training.
Antique blades — anything over 100 years old — shouldn’t be sharpened by amateurs. Patina, geometry, historical value. All of it can be destroyed. Museums and serious collectors use professionals. If you own an antique, treat it that way.
frequently asked questions
What angle do you sharpen a katana at?
10 to 15 degrees per side. Lay the blade flat on the stone. Slide two or three coins under the spine. That’s roughly 10 to 12 degrees.
What grit whetstone for a katana?
400 to 600 grit for damaged edges. 1000 grit for maintenance. 3000 to 5000 for refining. 8000 or higher for final polish. Don’t skip grits.
Can I use a pull-through sharpener on a katana?
No. Pull-through sharpeners are for kitchen knives. They remove too much metal and can’t follow the curve of a katana blade. Use whetstones.
How often should I sharpen my katana?
Display blades: once a year or less. Regular cutting practice: every few months. Strop between sharpenings.
What is choji oil?
Traditional Japanese blade oil. Clove oil mixed with mineral oil. Any light mineral oil works as a substitute.
Will sharpening remove the hamon?
Not if done correctly. The hamon comes from heat treatment, not surface pattern. Stay on the edge side of the hamon line. Light pressure.
Sharpening vs togi?
Sharpening maintains the cutting edge. Togi is the full art of Japanese sword polishing. Trained professionals. Dozens of specialized stones. Sharpening is maintenance. Togi is restoration.