Yep, most ceramic coffee cups and bowls have an unglazed ring around the bottom where they sat in a kiln being fired when they were made.I had no trouble finding a couple coffee cups to experiment with. A couple years of buying knives without progressing my sharpening skills has left me in a bind. I now have all these dull knives.
After watching lots of YouTube videos and reading what blog posts I could find, my technique developed to the point where I can now sharpen just about all my knives to a hair popping edge with any random coffee cup. I have even shown friends and family this trick. Though I am still mastering other systems like my EZE-LAP and the Japanese whetstone.
The technique I use is simple: First I choose the correct angle by looking at the side of the edge I am working on and rolling the knife down until it his the angle I want. This concept is central to all hand sharpening so I won't get into it now. Also, I don't seem particularly skilled at getting the exact angle by eye, so I also feel for that friction point where the entire edge is on the ceramic surface of the cup.
Some folks like to point out not to press too hard on the knife, which is correct. But I had the opposite problem, so once I started pressing a little harder and using a sawing motion, I got immediate results. Where it would take me 10 minutes to sharpen a knife, now it's just a few strokes on each side of the blade.
How do you know how much time to spend on each side of the edge? I've seen videos talk about looking for a "micro edge" or "burr" but maybe my eyes aren't that good. What I look for is the shiny sheen of a new edge that has never seen the air. Another technique is to draw on the edge with a permanent marker and make sure you are removing the ink when you sharpen. I just look for that shiny edge, and I also look at the angle on each side and make sure I'm not putting different angles on each side, which I tend to do.
In fact, not putting the same angle on each side turned out to be the biggest flaw in my technique, and now I am vigilant about getting them as close to each other as possible. But it's important to remember with all hand sharpening that the exact angles do not matter. What matters is that you are building a good edge.
Because my eyes are getting old, the easiest way for me to tell that I'm building a good edge is to saw a few times, test the edge, and flip the knife over and saw a few more times. After the second sawing, did it get sharper? So, I look at the angles as best I can with my eyes, but I also go by the feel of the edge and I make note of how the edge is evolving.
Some folks say to go for an angle of 20 degrees and that sounds right, but I always seem to end up at a little less, maybe 17 or 18. But again, the exact angle doesn't matter as long as you are getting close enough to the same angle on each side. What I like about having my EZE-LAP system as a backup is that I can re-profile a knife to an exact angle if I screw it up by hand sharpening. Once you 'mangle the angle' by hand sharpening, it's hard (but not impossible) to put it back by hand, and using something with a machine set angle makes it a little easier to correct. So far I haven't used it to correct my mistakes, but it's nice knowing that the EZE-LAP is standing by.
|EZE-LAP angled sharpening system|
|The EZE-LAP works best in a vise|