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- Apr 27, 1999
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I will quote my response to a similar previous thread:
This is expected behavior for straight razors so it should be true for very fine edges honed at a very acute angle. The surface of a metal is much less stable than the interior. When you hone or machine the material you remove atoms from the surface and expose atoms that previously were surrounded by others of their kinds. Previously they were nestled in a reasonably uniform lattice of similar atoms (in a balanced state) now they are only connected on one side. This is an unstable (aka high energy) state. This surface will try and capture dirt and water molecules and is even inclined to move a little (relax) to a more balanced condition. The apex of an acute edge is the most unstable part of a honed surface. It is almost all surface and it is exposed all around and supported very little. It will try and relax through a lot of different mechanisms.
We think of edges as simple and ideal and the honing process as clean and without creating undo stresses. In reality there is always some degree of roughness to a honed surface and the honing process removes material through local overstress of the bonds between the metal atoms. We have left a high energy surface with minor damage to the underlaying structure. We have done something similar to sanding wood and we can expect the grain structure to rebound somewhat. It can particularly shift in spots where there are peaks in the surface structure that are adjacent to overstressed bonds in the underlying lattice.
So what is the common wisdom of centuries of straight razor users? After honing or using a razor it is expected that the edge will be damaged. There will be microscopic dings in the edge. These dings will exhibit ragged burrs and spurs that don't align with the intended edge. They will also be somewhat brittle due to work hardening (lattice dislocations) during the honing or use that created the dings. You are advised not to use or strop your razor at this time. Stropping or working the edge at this time will cause the edge spurs to break off. You are supposed to let your razor rest for a couple of days (you should have two razors) and then you strop just before you use it. The wisdom is that the edge will have relaxed, somewhat realigned itself and will have grown a trifle less brittle, during the two days. When you strop then the burrs and spurs will not break off and the edge can be reformed close to true. You are supposed to use the razor before it moves again.
I think that when you put away a freshly honed acute knife edge it will relax somewhat randomly over time. Remnant stresses of honing will get relieved through a mixture of movement, oxidation, and absorption of moisture through the air. For example stainless steel resists oxidation by forming a thin oxide coating (when fresh it does oxidize) to prevent open-ended oxidation (rusting). After honing, the first thing a stainless edge does is to rebuild an oxide layer. It will also absorb a mono molecular layer of water on its surface. It will want to absorb any other chemical that you have handy.
Frequent light honing may help you create a more stable edge. Another trick is to lightly strop your blade periodically starting a couple days after honing. So I do believe in edges doing funny things when you aren't looking.
This is expected behavior for straight razors so it should be true for very fine edges honed at a very acute angle. The surface of a metal is much less stable than the interior. When you hone or machine the material you remove atoms from the surface and expose atoms that previously were surrounded by others of their kinds. Previously they were nestled in a reasonably uniform lattice of similar atoms (in a balanced state) now they are only connected on one side. This is an unstable (aka high energy) state. This surface will try and capture dirt and water molecules and is even inclined to move a little (relax) to a more balanced condition. The apex of an acute edge is the most unstable part of a honed surface. It is almost all surface and it is exposed all around and supported very little. It will try and relax through a lot of different mechanisms.
We think of edges as simple and ideal and the honing process as clean and without creating undo stresses. In reality there is always some degree of roughness to a honed surface and the honing process removes material through local overstress of the bonds between the metal atoms. We have left a high energy surface with minor damage to the underlaying structure. We have done something similar to sanding wood and we can expect the grain structure to rebound somewhat. It can particularly shift in spots where there are peaks in the surface structure that are adjacent to overstressed bonds in the underlying lattice.
So what is the common wisdom of centuries of straight razor users? After honing or using a razor it is expected that the edge will be damaged. There will be microscopic dings in the edge. These dings will exhibit ragged burrs and spurs that don't align with the intended edge. They will also be somewhat brittle due to work hardening (lattice dislocations) during the honing or use that created the dings. You are advised not to use or strop your razor at this time. Stropping or working the edge at this time will cause the edge spurs to break off. You are supposed to let your razor rest for a couple of days (you should have two razors) and then you strop just before you use it. The wisdom is that the edge will have relaxed, somewhat realigned itself and will have grown a trifle less brittle, during the two days. When you strop then the burrs and spurs will not break off and the edge can be reformed close to true. You are supposed to use the razor before it moves again.
I think that when you put away a freshly honed acute knife edge it will relax somewhat randomly over time. Remnant stresses of honing will get relieved through a mixture of movement, oxidation, and absorption of moisture through the air. For example stainless steel resists oxidation by forming a thin oxide coating (when fresh it does oxidize) to prevent open-ended oxidation (rusting). After honing, the first thing a stainless edge does is to rebuild an oxide layer. It will also absorb a mono molecular layer of water on its surface. It will want to absorb any other chemical that you have handy.
Frequent light honing may help you create a more stable edge. Another trick is to lightly strop your blade periodically starting a couple days after honing. So I do believe in edges doing funny things when you aren't looking.
.
