Re: Why did old barber chairs have a 'strop' or leather strap?

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.