Thread: Sharpness of Straight vs DE & SE

Originally Posted by mparker762

Unfortunately my machine crashed so I lost the verhoeven paper and the 1920's popular mechanics article but that was one of the first things Verhoeven looked at. He compared a commercial razor blade (he didn't say if it was a DE or cartridge blade) and a straight razor that was honed by a guy he knew that still shaved with a straight. Both the commercial blade and straight razor averaged 0.5 microns across the edge as measured at 3000x with an electron microscope. The other interesting thing is that Verhoeven was able to get that same 0.5 micron edge with 9 micron diamond paste, an 8000 grit waterstone, and 0.5 micron diamond and chrome oxide. The finer grits simply gave him a higher level of polish and less variation in the cutting edge width along the blade. Oh and there were no serrations at the edge at anything finer than about 800 grit. You could see the grooves going down the bevel, but the cutting edge itself was formed where the steel finally got too thin and just kind of tore off. Softer steels couldn't take quite this fine of an edge, and steels around 63 rockwell could take very slightly finer edges (0.48 or some such).

The other interesting article is an article on the Schick website titled "Making of the Modern Blade" which mentions that they put the teflon coating on the blade specifically to reduce the cutting friction, which reduces the pulling sensation and improves the sensation of sharpness. This was a good clue that the reason the finer grit hones produce a better shaving edge is because the more polished edge causes less friction when cutting through the whisker.

And finally, the 1920's popular mechanics article examined the degradation of an edge across several days of shaving, both with and without stropping. They used a 3000x optical microscope to do this, so the pictures don't have the stunning clarity of Verhoeven's electron microscope, but the results were comparable. Their photos also show the torn-looking edge for example, and they were quite surprised by the lack of serrations or teeth. But most importantly these photos show that the main cause of dulling is corrosion and not wear. The stropping action knocks off the softer corrosion, exposing the pitted steel below, then further stropping polishes the underlying steel a bit. My suspicion is that one of the reasons razors gradually get to the point where stropping doesn't help is because the bevel near the edge gets corroded and pitted enough that the cutting friction is just too high, so you need the hone to cut the steel back past the pitting. Remember the cutting edge is also slicing through the top layer of skin, so it's exposed to a pretty harsh environment for steel. I suspect this is also why vintage razors sometimes need to be honed so much before they shave well - their edges are shot through with microscopic pinholes of rust, and it's not so much that they won't hold an edge (though this also happens) as they're simply too shot through to provide a polished low-friction bevel.

Two side-effects of studying this issue are that I've become much more appreciative of aggressive use of the linen strop, and a lot less critical of guys who use pastes. They're both a means to keep that edge polished, it just depends on whether you prefer the romanticism of the 19th century linen or the efficiency of 20th century industrial abrasives.

Exactly. The limit to edge sharpness is the type of steel the blade is made of. Both sharpening machine and honemeister are capable of reaching that limit.

If the best steels are only capable of a 0.5 micron edge, how sharp an edge can ceramics acheive? I know that diamond can acheive edges 1 atom thick based on an article that used a scanning tunneling microscope.