How To Test Knife Sharpness: 5 Best Ways

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The usefulness of a knife is dependent on the degree of sharpness the knife can boast. However, it is usually hard for some persons to decipher if their knives are sharp or not. The general belief is as long as it can cut through any object irrespective of the energy they exert, then the knife/blade is sharp. But this is not entirely true, as you waste time and energy making use of a blunt knife, compared to when you use a sharp knife that cuts through any degree of thickness seamlessly.

Therefore, it is crucial you know how sharp your knife is before you begin using them. This way your precious time is saved. So how do you ensure your knife is indeed sharp and ready for efficient use? In this article, we’ll be looking at how to test knife sharpness and maintenance.

Good Ways To Test Knife Sharpness

The most conclusive way to know if your knife is sharp is its ability to cut through a variety of objects, but then you’d need to begin work with it first before you can know this; at this time, you might have already damaged whatever you are doing at the time. This is why before using a knife for an important task, you should first test how sharp it is. Below are some of the ways to test the sharpness of your knife.

1. Paper Test

This is seen as “the oldest trick in the book.” And fortunately, it can be done using any piece of paper around you. You don’t need a special paper to carry out this test. To do this, get any piece of paper (clean and sturdy one, not weak), use your fingers to hold it in place, leaving a portion on top that your knife can slide into; next, slide the knife into that portion and pull it outward. If the knife is sharp enough, it will pass through the paper effortlessly slicing it into two clean sheets. A dull knife, however, will leave ragged edges on both slips. It can even cause a tear or perhaps slip off.

Another approach is to use a glossy magazine or a paper phone book. This method validates the sharpness of your knife because of the tricky nature of these types of paper. As a result, it is not easy to catch the paper with the knife edge. Therefore, a dull knife would not be able to do this smoothly. However, a sharp knife can do the job effortlessly when it is folded or rolled up. Surprisingly, toilet paper takes even more effort to cut neatly with a knife. So, if your knife can cut through it, then you can boost its sharpness at that point.

2. Shaving Test

This test is the next we will be considering. It is dangerous and so has to be done carefully, ensuring you don’t hurt yourself in the process. It involves using your knife to shave the hair underneath your arms. All you need to do is run the knife carefully along with the hairs on your arms, a sharp knife would clean out the hairs’ as you run the knife through it, but a dull knife leaves no impact whatsoever. You don’t have to touch your underarm skin as you do this, as that can cause a cut, especially if your knife is sharp. Don’t forget your underarm is the last place you would want to have an injury as it is uncomfortable.

3. The Onion and Tomato Test

Yes, you heard right. You can use your favorite kitchen ingredients; onion, and tomato, to test knife sharpness for you. For the onion test, it is generally agreed that any knife that can cut into the skin of the onion with little or no effort is sharp. However, if the blade is dull, it becomes a challenge to break the onion skin.

Meanwhile, for the tomato, the inside is soft and succulent, and naturally easy to cut. However, it has a tough outer flesh that is difficult to break. To test for sharpness, you don’t need any pressure whatsoever; place the knife on top of your tomato and den pull it back (retract your hand, without applying a downward force). If the knife can slice the tomato into two even with this action, then it is a sharp knife worthy of mention. A dull blade requires more force to cut through the skin, which can cause your tomato to break inside as you try to cut them into even chunks for cooking.

4. Finger Nail Test

If you are like me, and you don’t like any form of stress whatsoever, then this test is calling unto you. It comes in handy when you’re already seated and about to begin your knife tasks, and then you suddenly realize the need to check how sharp is the knife. At that moment, you don’t want to leave that spot to look for any of the materials discussed above, and so you use your fingernail, that is if you have a long one.

To do this, you can use either your thumb or your index finger. Place the edge of the knife gently on top of your fingernail, this way the knife is positioned perpendicularly to your finger. The proof of sharpness is ascertained when the knife can penetrate the fingernail without any pressure application from your end. However, if it slides off the fingernail, then it lacks a sharp edge and needs resharpening.

5. Visual Test

This test requires you to have fantastic eyesight, to be able to pick out the edge of the knife and decipher if it is sharp or not. There are two ways to go about this; you can choose to use a light source or a magnifying glass to assist your human eyes to see clearly. When using a light source, if you notice any form of reflection, then the knife is a dull one. However, if you notice a smooth uniform and straight black line, then your knife is sharp.

With a magnifying glass, you’ll need to look carefully at the blade side; if it appears in a black straight line, then it is sharp. For this purpose, the most suitable tool you can use is an electron microscope for scanning. However, they are expensive to obtain, and if the price is beyond your capacity, you can use a loupe and use it along with the light.

Other tests you can use are:

  • Hair whitling test– the knife should be able to slice off hair strands effortlessly with no stress.
  • Tongue test– Personally, I do not advise this, but if you’re bold enough, then by all means use your tongue to check if your knife is sharp enough. I hope you can enjoy your food afterward.

In Conclusion

Having a sharp knife or knife set is a necessity if you must finish your tasks easily and on time. This is not something that can be validated easily, and hence working in the kitchen, grocery store, or workshop can be frustrating. Do you want to know how to test knife sharpness? If yes, then this article was crafted for you. We have highlighted and discussed extensively the 5 best ways to test your knife sharpness and two additional methods. So, the next time you want to confirm your knife’s sharpness, think about either of these methods.


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