Secret #6: The Burr:
At this point we have a lot of good techniques. We should be able to grind a bevel very evenly and consistently along it’s entire length. We can check to see that we are grinding where we are supposed to and make corrections as necessary. There’s just one thing missing. How do we know when to stop? The answer, is secret #6, The Burr.
The burr has been discussed and detailed in a lot of sharpening literature. I’m just going to briefly cover what it is and then get to what I think is important. What is the burr? The burr is a curl of metal that forms when grinding reaches the edge. The burr is a positive indication that you have ground the bevel until it hit the apex. In most cases, this means you are done grinding on that side of the blade. Here’s a picture showing the burr forming on the opposite side from the grinding.
(from:
http://www.knifeplanet.net/wp-content/uploads/2015/10/raising-the-burr.jpg)
The burr tells you that you are done grinding. Form a burr on one side of the blade, full length. Then grind the other side of the blade until you get a second full length burr on the other side. Now remove the remaining burr. This tiny paragraph is a summary of a complete sharpening of a blade. That’s it.
If there’s a “secret” about the burr, it’s this: You must make a full length burr on each side of the edge in order to correctly grind the edge bevels. Full length is the important part here. Many people, myself included, check for a burr and as SOON as we detect a burr in one spot, we switch to the other side of the blade. This is wrong. Once you have a burr formed in one section of the edge, you should continue sharpening until you can detect the burr along the ENTIRE length of the blade. Use secret #5, selective grinding, to concentrate your work on the areas that don’t have a burr yet. Do blending strokes. At some point, you will probably be grinding an area less than 1 inch wide. The burr will have formed on the whole edge, except for this one section. Continue grinding in that area until you get a burr, or that part of the blade will never be truly sharp. This is the real secret of the burr.
The three important aspects of the burr are:
1. How to form a burr.
2. How to detect the burr.
3. How to remove the burr when you are done.
Forming a burr:
This is simple. Just keep grinding, using all of your tools and techniques, until the edge bevel reaches the apex and a burr will form. Keep going until you have a burr along the entire edge from heel to tip.
Detecting the burr:
There are many, many different ways of detecting this delicate curl of metal. Feeling with your finger tips seems to be the most popular way. Here are a few for you to try. If you need help with this, seek out other resources that detail burr detection. This is a HUGELY important part of sharpening, so you want to get it right.
A. Sliding your fingers off of the edge. Move your fingers from spine to edge on the blade, trying to feel the curl of the burr digging into your finger prints.
B. Testing for sharpness, both directions. Have you used your thumb to test a blade for sharpness by moving across the edge? You can use this to detect the burr. Stroke your thumb on the edge as normal feeling for sharpness. Now spin the blade around so the left and right sides of the blade swap places. Do your test for sharpness again. Did it feel sharper one way than the other? If so, the side that felt sharper has a burr. That’s because the burr is thinner than the real edge, and it digs into your finger prints more deeply. This works surprisingly well with a little experimentation.
C. The fingernail catch. Slide your fingernail from spine to edge on the blade. When it reaches the edge, it should just slide right off of the blade. If you have a nice big burr though, the burr will catch your fingernail and stop it. It’s sort of an amazing feeling actually. This is a very positive test that you pretty much can’t get a false positive from. It either catches your fingernail and stops it, or it doesn’t.
Burr Removal:
Once you’ve raised a burr on one side, switched sides, and then raised a full length burr on the opposite side, you want to remove the burr completely, leaving behind a clean crisp edge. Again, there are many many ways of doing this. Seek out another resource for more complete directions and techniques for burr removal. I’m just going to highlight a few that I like.
A. The double angle technique. Let’s say you’ve been sharpening at roughly 15 degrees per side. You’ve formed the burr twice and you’re ready to remove it. Put the side with the burr down on the stone. Now raise your angle to roughly 30 degrees. It doesn’t need to be exact at all. Just a much higher angle than you were using. Now, do 1 or 2 very, very light strokes. Not even the weight of the blade. Flip the blade over and do 1 very light stroke on that side. If you’ve done it correctly, the burr should be essentially gone from both sides. Check and see. If some burr remains do another single light stroke on the side with the burr and check again. Once it’s gone, lower the angle back down to the original and do one light stroke per side, switching sides after each stroke. Do perhaps 3 to 5 of these original angle strokes and your blade should be done.
B. Drawing through wood, cork, or felt. Just lightly running the length of the blade through end grain of wood, a wine cork, or hard packed felt can rip the burr off. This is most useful when the burr is very small or there are just little burr chunks remaining on the edge. Notice the gray or black residue that’s left on the cork or wood. Experiment with this and see how it works for you.
C. Deburring directly on the stone. If you are very careful with light strokes, you can remove the burr fully, at the original angle, just by using light pressure and checking after each stroke. Ken Schwartz advocates doing sideways strokes, parallel to the stone (not forward, not backwards, but sideways) to grind the burr off. I’ve had limited success with this and I only mention it because Ken is exceptionally skilled. I’ve had my best results removing the burr at the original angle by doing forward strokes only.
What if you can’t seem to form a burr? Use secret #4 observation. Use the reflected light technique to see if the blade edge is reflecting light. If it reflects light, it’s dull enough that more grinding is necessary to form a burr. Reflected light (directly on the edge) is a really good way to monitor your progress. Once the reflections disappear, you are very close to forming a burr.
Learn to detect the burr consistently. Work on making a full length burr every time you sharpen. On both sides. If you’ve never formed a full length burr before, you’re probably going to be rather surprised by the resulting edge. I know the first time I did it, it changed everything for me. I couldn’t believe that I just hadn’t been grinding for long enough. My edges improved markedly once I got this figured out.
Learn to deburr fully. This can be tricky. If my example methods above don’t work well for you, seek out the advice and techniques of others. Burr removal is absolutely essential to forming clean, crisp, durable edges.
Master this and you’ll be well on your way to making outstanding edges.