how do sharpening knives work?

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I’ve heard someone say that there is a difference between actually sharpening a knife and making it not dull with a rod or something. What is the difference?

In: Technology
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I think you might mean the difference between sharpening a blade and honing it with a honing rod, the latter straightens out tiny knicks and dents in the blade

When a knife is used, the edge accumulates damage over time by either chipping off or bending over to a side.

When you use a rod on a knife, you’re just pushing all the bits that are bent back towards the center. There won’t be an impact to any parts of the blade that are chipped.

When you sharpen a knife, you’re removing material from the edge to create a new edge. If there are any bits of the blade that are chipped, they’ll be removed via the sharpening process.

When I knife gets “dull”, one of two things is happening.

– The edge of the knife is still sharp, but it has bent or rolled slightly to one side or the other. [Here is a picture](https://www.globeequipment.com/learning-center/wp-content/uploads/2018/02/Victorinox_Honing-Graphic-1.jpg). This is known as the knife being out of ‘true’ – it isn’t _actually_ dull because the edge is still there – and can be corrected with a honing steel. By gliding the knife down the steel, the edge is bent back to true which improves performance. This is known as honing – **not** sharpening.

– The edge of the knife is worn down and is no longer sharp. [Here is another picture](https://cdn.shopify.com/s/files/1/0017/6632/6345/files/dull_knife_sharp_knife_compare.jpg?v=1553939104). No amount of honing will fix this because the edge is actually gone. You have to sharpen this knife – remove material from the cutting edge to get it back sharp again. **This** is sharpening.

Imagine zooming waaaaaay in on the edge of a knife. Not for real – keep those blades away from your eyes! – but in your imagination. Imagine looking at the front of the blade, and zooming in so close that the edge of the knife is a tall, skinny triangle.

Two things can happen when you use the knife:

* The tip of that triangle can get shoved over to the side, due to being pushed against the cutting board (or whatever you’re cutting). You fix this by **honing** it – using that rod you mentioned to just shove the tip back into alignment.
* You can easily hone a knife yourself, and there’s no harm in doing it often.
* The tip of that triangle can get worn down, so now it’s rounded instead of pointy. No amount of shoving that edge around will help – if it’s rounded, then it’s rounded no matter how you hone it. You fix this by **sharpening** it, which involves literally grinding away at the blade and removing the sides of the rounded-off edge to make it a sharp triangle-tip again.
* Yes, this means the knife technically gets a little smaller each time it’s sharpened. If you keep sharpening it often enough, eventually you’ll have no more knife left.
* You can *not* easily do this yourself; it requires training and experience. Luckily it doesn’t have to be done often at all (for the average home cook).