What makes a good knife?
A really great knife is balanced so that it sits in your hand comfortably; lightweight so that you can use it longer without fatigue; sharp so that it cuts smoothly and cleanly; and beautiful in a way that makes you want to have it on display, not hidden in a drawer.
- Blade thickness is important for creating a sharp blade. Thinner blades will slice through soft things more easily. This is because of how much resistance is created - thinner blades have less surface area in contact with the thing you’re chopping, and so they go through more easily. Think about how a paddle works - if you turn the paddle sideways it will slice through water easily, with very little resistance; but if you turn the paddle flat it will resist pushing through the water enough to propel the boat forwards. For knives, having thinner blades makes chopping vegetables and meat easier and gives the feeling of smoothly and easily gliding through, so you don’t need to push hard.
Hardness: Hardness is a technical term for the degree to which a material is able to be scratched, or indented, when pushed on by something else. Very hard materials resist pressure very well; whereas softer materials are easily able to be indented or scratched.
- What’s good about hardness: When one material is harder than another, and you push them together, the harder material will go through the softer one - like a knife through butter. The knife is hard, the butter is soft. A harder knife will go through more easily and will hold its sharp edge for longer.
- What’s bad about hardness: When a material is very hard, it usually is also quite brittle - glass is a great example of this. Glass is difficult to indent or scratch, but if you push too hard it will shatter or snap. Steel is the same. A harder knife will also be more brittle and more prone to snapping, or chipping.
- For knife steel, hardness is usually measured on the Rockwell Scale (HRC). Most steels used for knife blades fall within a range of HRC 50-65. A lower number is softer and a higher number is harder.
- Whether a number is ‘good’ or not is mostly about what you want to use the knife for. If you want to cut soft things like vegetables or meat then a harder knife will stay sharp longer and cut more easily. If you want to cut harder things like bones or coconuts, then you will want a softer steel (lower HRC) so it won’t chip as easily.
- Incidentally, the hardness of our knives is why we recommend using a good chopping board - a softer board will decrease the chance of chipping or breaking your knife. Be careful with cutting on a ceramic plate or stone benchtop - these are very hard materials and will increase the chance of chipping or breaking the blade of your knife.
Toughness: Tough materials can absorb a lot of force without breaking or fracturing. The opposite of tough is brittle. Very tough materials like rubber can withstand being hit by a hammer (lots of force) without breaking; whereas a material like glass, which is brittle, will break easily if hit with force.
- What’s good about toughness: when something is tough it doesn’t break easily. This is especially important when you want to be able to handle an object without needing to be very careful with it. Think about the difference between how you might handle a rubber ball vs a glass ball. You would happily throw a rubber ball against the wall; doing the same with the glass ball would not go well. For knives, the more you are rough with chopping, the more you will want a tough knife.
- What’s bad about toughness: materials that are tough are able to bend before they break. This also means that the material gives more when it comes in contact with other materials. For a knife, this translates into faster dulling. A tougher knife will withstand more knocks, and it will also need to be sharpened more often, and will not be able to get as sharp.
- A really sharp blade is created primarily by the thickness (or thinness) of the blade, and the hardness of the steel and the sharpening angle.
- Thin blades are able to be sharper, because the cutting edge is a more acute angle, allowing for a smaller surface area. Small surface areas require less force to be pushed through something else.
- Our blades are less than half the width of standard Western style knives, allowing them to be twice as sharp.
- The hardness of the steel prevents the edge of the blade from rolling over, enabling the knife to stay sharp longer. Knives become blunt due to the cutting edge being eroded or rolled over as you chop. A harder steel will stay sharp longer.
- Blade weight to handle weight.
- Rust resistance is how quickly or easily a blade will start to form rust if left wet. Whether a blade rusts easily or not is caused by which elements the metal is made from. Metals with a higher content of chromium will resist rust better.