Discover easy, step-by-step methods to fix common Japanese knife issues like chips, rust, and dull blades. Learn how to maintain and restore your knife’s sharpness using beginner-friendly tools!

Beginner’s Guide: Fixing and Repairing Your Japanese Knife, Part 1

Japanese knives are famous for their sharpness, precision, and excellent craftsmanship, making them a favorite among both home cooks and professional chefs. But even the best knives can get damaged over time, such as having a chipped blade, a dull edge, or rust spots.

Taking care of your knife properly is crucial to keeping it in top shape, but fixing common problems can seem tricky if you're new to it. This guide will show you easy, step-by-step ways to fix issues like chips, rust, and more, so your knife stays sharp and effective for years to come!

Table of contents

1. Common types of damage in Japanese knives
1. Chipped blade
2. Dull edge
3. Rust

Common Types of Damage in Japanese Knives

Chipped Blade

Chipped blades can happen to even the best knives, often because of how Japanese knives are made. Most Japanese kitchen knives use very hard steels, measuring over 60 HRC (for comparison, Western kitchen knives usually max out at 55 HRC). This hardness helps the knives stay sharp, maintain a thin profile, and stay light. However, it also means the blade can be very sensitive and more likely to chip if not used properly.

How do chips on a Japanese kitchen knife happen? Japanese knives are built to handle vertical force well but struggle with lateral force (side pressure), which can lead to chips in the blade.

Common causes of chips in knives: 

1. Cutting frozen food can damage your knife: Cutting frozen items, bones, and other very hard ingredients can easily chip the blade. It’s best to avoid cutting these types of food with your knife.
   
   If you find yourself working with these ingredients often, you may be in need of a specialized knife. Be sure to check out parts one and two of our articles on specialized knives!

2. Using the wrong cutting board can chip your blade: Cutting on very hard surfaces like stone, glass, or extremely hard wood can dull your knife quickly and potentially cause chips. 

As a solution, consider using Musashi Japan’s cutting board. Our boards are made from shimanto hinoki, a type of Japanese cedar that is at least 90 years old, giving it a tight grain pattern. The hinoki wood surface, known as kiomote, is edged with walnut to prevent twisting and warping. 

3. Dropping your knife can break the tip: When dropped, the tip of the knife is often the first part to break. 

4. Oversharpening can occur with your knife: Sharpening a knife at too small of an angle can create a very thin edge that can’t handle the pressure when the knife hits the cutting board, leading to chips. Beginners may find it better to have professionals sharpen their knives rather than doing it themselves.

Check out our sharpening guide to help prevent chips when sharpening.

How do chips in a Japanese kitchen knife affect knife performance? While high-HRC chef knives offer great benefits, they are generally more sensitive. A chip, no matter how small, can affect your knife’s performance. It might make cutting less effective and result in uneven slices or crushed food. Uneven slicing can impact your cooking quality, causing smaller pieces to overcook while larger pieces stay undercooked.

How can I repair a chipped Japanese Knife?

To fix chips in your knife, you'll need a coarse whetstone or a diamond plate. Start by grinding the knife at a 90-degree angle to the stone. This method is the quickest but will slightly change the knife’s shape, making it thicker. If you’re okay with this, you can use this method. But if you want to keep the knife’s original shape, you might need to thin it out afterward to get back to its original profile.

For dealing with chips, use sharpening stones with a grit level of less than 1,000. Here’s a step-by-step guide:

1. Start with a coarse stone: Use a stone with 120 or 220 grit to remove the major damage.
2. Move to a medium stone: Use a stone with 320 or 500 grit to refine the edge.
3. Finish with a fine stone: Use a stone with 800 grit or higher to polish the blade.

Musashi Japan offers a range of professional-grade sharpening stones on our website!

Stone	Grit level	Description	Recommendation
Rough	< 1,000	Grit less than 1,000 is ideal for reshaping a chipped and/or cracked large-edged knife.	Sharpening Stone #400 Professional Sharpening Stone #500
Medium	1,000-3,000	Grit between 1,000-3,000 is a good starting point for first-time sharpeners to sharpen noticeably dull knives.	Knife Sharpener #1000 Knife Sharpener #3000 Professional Sharpening Stone #1000 Recommended! (Dual Sided) Professional Sharpening Stone #1000/#4000  Recommended! (Dual Sided) Professional Sharpening Stone #1000/#6000
Fine	3,000-6,000	Grit between 3,000-6000 should be used after sharpening on a medium-sized stone to adjust the edge of your chef’s knife.	Sharpening Stone #3000 Sharpening Stone #4000 Professional Sharpening Stone #6000
Near Mirror Polish	6,000-10,000	Grit between 6,000-10,000 provides a near-perfect edge, leaving your knife’s edge polished to the naked eye.	Professional Sharpening Stone #8000 Professional Sharpening Stone #9000
Mirror Polish	10,000+	Grit past 10,000+ provides the sharpest edge possible. This requires considerable time and effort, but gives your knife a mirror-like edge without any visible flaws.	Professional Sharpening Stone #12000

Dull Blade

A dull knife isn’t always a sign of misuse or poor care; it’s often just a natural result of time and regular use. This actually means your knife is being used as it should be. Over time, the constant friction and cutting tasks will naturally make the knife lose its sharpness. This is completely normal and not something to worry about. A well-used knife is doing its job right! Regular maintenance, including sharpening, is key to keeping your knife in top shape and ensuring it remains a reliable tool in your kitchen. 

How do knives become dull? With use, the edge of the knife can start to fold over when it encounters resistance from the food or the cutting surface. Over time, this makes the blade become overall dull.

How does a dull blade in a Japanese kitchen knife affect knife performance? A dull knife can make cooking more difficult in several ways:

1. More force needed: A dull blade requires more effort to cut through ingredients, making cooking less efficient and more tiring.
2. Less precision: A dull knife doesn’t cut as accurately, which can affect the presentation and quality of your dishes.
3. Increased risk of accidents: Dull knives are more likely to slip off the food, which can lead to accidents and injuries.
4. Uneven cuts: Dull knives can cause uneven cuts, which may lead to inconsistent cooking times and affect the texture and flavor of your food.
5. Crushing delicate items: Instead of slicing cleanly, a dull knife may crush or tear delicate ingredients.

Keeping your chef’s knife sharp is essential for efficiency, safety, and achieving high-quality cooking results.

How can I repair a dull Japanese Knife?

If your Japanese knife has become blunt, the best solution is to sharpen it. Sharpening restores the knife's edge, making it as effective as it was when you first got it. There are several ways to sharpen a knife, like using a diamond plate, depending on your preference and the tools you have available.

The tool you will most likely already own is a sharpening stone. To repair a Japanese style knife’s dull blade, you can follow this process:

1. Honing: Place your honing rod on the cutting board with the handle up. Swipe the knife from base to tip with even pressure, doing 3-4 swipes per side. Hone regularly to maintain sharpness; sharpening should follow as needed.
2. Sharpening: Position the blade flat on the medium sharpening stone at a 45-degree angle. Add water and sharpen until sludge forms. Sharpen the face side about 7 times and the reverse side 3 times. Continue until the edge is sharp, finishing with the reverse side.
3. Check for burr: Run your finger along the blade to detect a burr, which indicates sufficient sharpening. Remove the burr by sharpening the reverse side until it disappears.
4. Strengthen the edge: Lift the knife slightly and sharpen the tip a few times to strengthen the edge, known as Kobadome.

Regardless of the method you choose, regular sharpening is important to maintain the performance and longevity of your knife. A sharp knife not only makes your cooking more efficient and enjoyable but also ensures safety and precision in your kitchen tasks.

For more details, watch our YouTube video on knife sharpening or refer to our beginner-friendly sharpening guide!

Rust

It's normal for knives to rust over time, and eventually, every knife owner will face this issue. No matter how well you care for your knife, rust can still develop. When you notice rust starting to appear, it's important to address it right away because letting it sit will only make it worse.

How does rust form on a Japanese kitchen knife? Rust forms when water and oxygen come into contact with the knife. If only one of these is present, rust is less likely to happen. But when both are present, rust can develop over time.

Common causes of rust:

• Leaving the knife in a humid room
• Forgetting the knife in the sink or letting it sit in water
• Storing the knife while it’s still wet
• Cutting acidic foods (like tomatoes) and not cleaning the blade right away

How does rust affect a Japanese kitchen knife? Rust can significantly impact your knife's performance and the quality of your cooking. Here’s how:

• Cutting efficiency: Rust can make the knife less sharp and efficient. A rusty blade might have a rough edge that tears rather than slices through food cleanly, affecting the texture and appearance of your dishes.
• Hygiene: Rusty blades can harbor bacteria and contaminants, which might transfer to your food and pose a health risk. Additionally, rust can give food an unpleasant metallic taste.
• Kitchen efficiency: Using a rusted knife can slow down food preparation and make tasks more laborious and less precise, impacting your overall kitchen efficiency.

How can I repair a rusty Japanese Knife?

Rust not only looks bad but also makes your knife unusable. Here’s how to remove rust and restore your knife:

1. Using a sharpening stone: A medium or fine sharpening stone can help remove rust while also sharpening the blade.

2. Using other specialized tools: A rust eraser or similar tool can be effective for scrubbing off rust.
   
   Oil or eraser – which one should you use? To actively prevent rust, especially on carbon steel knives, use Tsubaki oil. For rust that has already developed, a rust eraser is a good tool to remove it.
   
   You can find and purchase both Tsubaki oil and rust erasers on our website! 

3. Using vinegar and baking soda: Soak the knife in a solution of white vinegar or apply a baking soda paste for 5 to 10 minutes. After soaking, wipe down the rusted areas with a cloth or sponge. For stubborn rust, you may need to use steel wool.

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