|MadSci Network: Science History|
It isn't easy to find information about leather strops (as you found out). The answer to your question lies in an understanding of what happens at the sharp edge of a razor. During the normal process of cutting something, the sharp edge tends to bend, often curling in one direction or the other. Sometimes little burrs or nicks will also dull the cutting edge. The straight razor was stroked along the length of the strop, with the sharp edge of the razor trailing the motion of the razor (in other words, the razor was moved in the direction opposite it's cutting direction). As the razor moved along the strop, the heavy leather tended to bend the curled edges and burrs back in the proper direction. The stroking motion was alternated on each side of the razor and gradually would line up the cutting edge. In addition, I suspect that there was also some polishing taking place at the same time. When metal is polished, it is often held against a soft buffing wheel where a combination of wax and fine ceramic particles produce a polishing effect. I'd bet that the strop produced a similar effect. As to sharpening knives, the Boy Scout Handbook gave a pretty good explaination of proper technique for using a whet stone when I last looked. The action of a whet stone is to grind away at the metal of the knife. Stones are going to differ based upon their abrasive properties and average particle size. Obviously even though a stone is hard, unless it has the right type of granular texture, it isn't going to be very effective at removing the metal from the surface being polished. Generally some sort of lubrication is added to help spread around the abrasive particles from the stone as the grinding action wears the stone down. Companies like Norton Abrasives generate hundreds of million dollars in sales by knowing the answers to these types of questions.
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