The Why and How of Sharpness
There are a couple things to consider when figuring out how to test for sharpness and to answer the question 'Why isn't my knife sharp?' when using a Wicked Edge.
The first is to know that sharpness isn't one specific result. Sharpness is completely dependent on the task you're trying to do. For example, a straight razor and axe are both sharp in their respective realms but try to use a straight razor to chop wood or an axe to shave, and the results will be less than stellar. Sharpness should be measured in how well the edge performs at the specific task you're creating it for. Not all sharp blades will perform well with every test. A very refined, low angle will perform well with a paper cutting test, but won't break down cardboard or cut through zip-ties easily. A super toothy edge will give you paper-thin tomato slices but won't be very useful for creating a feather stick. Make sure the angle and edge finish match the type of cutting task you'll be performing. You can find out more about which finish is best for you in this article.
The second thing to consider is 'Are you actually sharpening all the way to the apex of the edge.' This question revolves around ensuring you're creating a burr and fully forming the apex of the edge down the entire length of the blade. The burr confirms that you are shaping and refining the edge itself, not just the bevel. To form a burr, you need to utilize the marker method to make sure you're at the correct angle and sweet spot. You can find out more about what a burr is as well as how to create it and find it in this article. It's safe to say that if you don't fully draw a burr down both sides of your blade, you will never be able to have a truly Wicked Edge.
The last thing you want to consider if you're not getting a knife as sharp as you'd like is how broken in are your stones. Diamond Stones need to be broken in before they perform at their best. You can find out more about Diamond Stones here. If your stones aren't fully broken in, you're creating deeper, more jagged edges than you'll be able to see with the naked eye. If you're simply putting a working edge on a blade and just need it to cut through cardboard, tape, etc, you'll notice this a lot less. If you're looking for a super-refined edge that needs to be clean, you'll notice that difference almost immediately. You can see the differences in the images below where the scratch pattern from a broken-in stone is much cleaner, smaller, and smoother. The image of the not broken-in stone is rough, deeper, and much more jagged.
Scratch patterns from a fully broken-in 600 Grit Diamond Stone
Scratch patterns from a not broken-in 600 Grit Diamond Stone
If you're interested in figuring out how to tell if your blade is sharp, below is a list of methods for testing sharpness:
- The most basic one is to test if the edge 'bites' into your nail or a marker. When you've finished sharpening, keep your blade in the vise and rest your fingernail or a marker on the edge at a 45-degree angle. Gently pull down and see if you can feel the edge bite in and prevent you from pulling your nail or marker down. Test this all the way down your edge. If your nail or marker slips easily off the edge, you have a flat spot and need to recreate a burr in that section. No matter the level of refinement, this test will work and will give you a good idea if your blade has an edge.
- Paper cutting test. There are a few ways to do this test and both will provide the best results if you have a fairly low angle (sub 20 degrees) and a more refined edge (1000 grit or above). You can either take the paper in one hand and push the knife into it, trying to get very thin slices. If your edge is very refined, you should be able to cut curves into the paper with very clean cuts. The other option is to fold the paper like an accordion and stand it up on a flat workspace. Then take your blade and gently push it straight down, trying to cut the paper cleanly without sawing the knife. Again, a very refined, low angle works best for this specific test. Most people use notebook or printer paper but if you're feeling really confident about your edge, newspaper will show just how refined your edge is.
- Shaving arm hair. This isn't the best option as we've seen people at trade shows cut themselves pretty good, but if your edge is low enough and refined enough, you should be able to cleanly shave the hair off your arm in one pass.
- The hanging hair test. This test is most often done with straight razors to ensure edge 'pops' hair. The idea is that the edge is so refined and so sharp that the hair literally 'pops' as soon as it touches the edge. You can see a great example of it below:
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