What exactly is ‘sharp’?
Sharpness has always fascinated me. The origin of my passion for knife making and the catalyst for becoming a knife maker was the topic of knife sharpening. This was over twelve years ago, and it remains an integral part of my work to this day. It is not sufficient for me to briefly draw a finished knife across a grinding belt. I sharpen every knife manually, either on a guided sharpening system or on bench stones, to guarantee maximum sharpness and a cutting edge that isn't overheated. (And before that, the blade is of course ground wet under flood cooling.)
But what exactly happens when sharpening a cutting edge? Hundreds of YouTube channels, blogs and veteran knife makers have already pondered on this question and have produced a vast pool of knowledge. What was missing however, was a (public) investigation of this topic using a high-resolution scanning electron microscope in the actual nanometre range. It is nothing new to observe cutting edges under a scanning electron microscope, that has been done before many times. There is already plenty of material on this topic on the internet and in academic literature. However, no one has yet been able to tackle the subject of knife sharpening with a magnification of hundreds of thousands or even more, i.e. with true nanometre resolution. Until now!
Thanks to my very good friend Dr. Marvin Groeb from Germany, who has access to a Zeiss Gemini SEM560 scanning electron microscope for professional reasons, the knife community has gained fantastic new insights into the topic of knife sharpening in recent months. Marvin, usually just called Marv, started his own blog about a year ago, where he posts articles on everything related to knife sharpening with remarkable frequency and in excellent quality. (By the way, he also sells the best diamond sharpening stones currently on the market, but I'll be doing a separate YouTube video on that in the near future.)
Last November, I had the opportunity to visit Marv in his lab. In my luggage: some of my custom knives made of Vanadis 8 steel with a hardness of 66 HRC. Our opening question on the vast topic of “sharpness”: What actually happens when you strop on leather with diamond paste?
Below you will find the article (in English, but autotranslate works great these days) on Marvin's blog. Be sure to check out Marvin's blog while you're there. It's worth it! Enjoy reading.
https://drmarv.com/2025/11/19/musings-about-material-removal-stropping-is-dead-or-is-it-part-1/