Even the most high-quality kitchen knife won’t perform well once an edge becomes dull. We all know the importance of periodically sharpening your knives to maintain their cutting edge. As you do this, it can be difficult to tell when your knife is sufficiently sharp, leading to over sharpening and unnecessary blade loss or damage. A common misconception is that the more you sharpen a knife, the sharper it will get. However, this is simply not true. Over-sharpening can actually damage the knife edge and ultimately make it duller.
The Best Methods for Testing Knife Sharpness
There are several methods to help determine whether a knife blade is sharp. These methods range from simple at-home tests with items you have around the house to professional sharpness testers that can measure and quantify the sharpness of your knife. Each option will help you determine when a blade is sufficiently sharp, ensuring that your knife performs effectively and safely.
Let’s take a look at some of the most common knife sharpness tests used today:
Visual Inspection
A simple method and one we recommend starting with first is a visual inspection of the blade edge to determine its level of sharpness. Examining under a bright light can show nicks, chips, and other imperfections that lead to a dull knife and reduced performance. Your sense of touch can also be another indicator of deformities. Very carefully run your finger along the knife’s edge and feel for rough spots, dents, or other inconsistencies. Finding these problem areas before moving on to other methods can help you address any damage that may need repair or sharpening, preparing the knife for further testing.
The Tomato Test
Cutting a tomato is the ultimate test of a knife’s sharpness. Their thin slick skin, rounded surfaces and delicate insides are hard to slice with finesse using anything but the sharpest of edges. A sharp knife will glide through the skin without crushing, bruising, or destroying the insides. If you find yourself using too much downward pressure and doing a sawing motion, this also indicates that your knife is too dull.
The Paper Test
An alternative method to test the sharpness of a knife is to try slicing a piece of paper. You just need a standard piece of white printer paper, which makes this check a simple one to do. To carry out this test, hold the paper out in one hand and attempt to move your knife through it starting from one of its edges. A sharp knife will glide cleanly through the paper, while a dull one will instead leave a jagged cut or fail to make a slice at all.
Should you want to go further with this paper test, you can use a page from a magazine as well. Magazine paper is smoother than normal paper, making it more slippery. You can choose to follow the same process as you do with printer paper when performing the cut. Alternatively, you can roll the magazine paper into a tube before trying to slice it. Either way, if your knife passes through the paper effectively, you’ll know that you’ve achieved maximum sharpness.
The Shaving Test
Another simple way to determine blade sharpness is to attempt to shave hair on your hand or forearm. Before beginning this test, it’s crucial to follow a few necessary precautions to ensure safety. Make sure you’re in a well-lit area, the blade is completely clean and dry, and you have a firm grip on the handle and understand proper cutting techniques.
When ready, hold the knife at a 30-degree angle to the surface of the hair. The blade should only make contact with the hair and not the skin. Next, gently guide the blade along the hair, in the direction of hair growth, and observe whether the blade cleanly shaves. A razor-sharp blade will shave arm hair effortlessly. A dull blade will often only pull, snag, or glide over the hair, indicating more knife sharpening is needed.
The Fingernail Test
Testing a blade’s sharpness can also be performed with nothing more than your fingernail. As with all other tests, always exercise caution with this method to avoid injury. To perform the fingernail test, grip the knife firmly, gently place the edge against one of your fingernails at a slight angle, and very lightly tap the fingernail. A sharp edge will “bite” into the nail, catching slightly without much pressure, while a dull blade will slide off without catching. Repeat this along different parts of the blade to check for consistent sharpness from tip to heel.
The Thumb Test
Feeling the knife blade with your thumb is another way to determine edge sharpness. This involves running the pad of your thumb perpendicular to the blade, not along the edge. A sharp knife will feel smooth and slightly “grab” or catch against the skin on your thumb. A dull blade will most likely feel slippery or blunt.
The method, like several others, requires direct contact with the blade so always use caution and be gentle and deliberate to avoid injury. This method should only be attempted by those comfortable handling knives.
Professional Tools
For those who prefer a professional solution that provides a more objective way to measure knife sharpness, sharpness test kits are ideal. These kits often come with everything you need, including test media, stands, and measurement devices, designed to assess the sharpness of a blade accurately. After following the simple step-by-step instructions, you’ll be able to gauge the effectiveness of your sharpening process, with reliable benchmarks. Sharpness test kits are easy to use and can help identify any areas that may need further honing, providing sharper edges and peak performance.
Shop our Selection of Japanese Knives and Sharpening Accessories
Understanding and applying the right methods to test the sharpness of your knives ensures they perform optimally and safely. If your knife fails any of these tests, be sure to check out our Japanese Whetstones to bring your knife back to optimal condition, and don’t forget to shop our wide range of handmade Japanese knives and supplies for both professional and home chefs.