Sufi,

Thank you for posting your observations. I've found that using a diamond sharpening rod works well, especially with warped blades. I'm actually more comfortable using rod-shaped sharpeners because I have much more experience using them. The thing to keep in mind with any shape of sharpening device is to use very, very light pressure as the blade gets sharper to avoid tearout of the fine edge. This is even more important with curved ones like slipstones and such because of the small point of contact. They sure can sharpen quickly though!

Jeff