Quote Originally Posted by Utopian View Post
I touch a lathered brush to a wet hone and transfer just enough lather to break the surface tension of the water so that I have a uniform layer of lathered water on the hone.
I'm a bit surprised that Ron's response is the only one mentioning surface tension so far. Soap changes the surface tension ('breaks' it, for lack of a better way to put it), so if anything, the buffer zone between hone and steel would be less rather than more when compared to plain water i.e. plain water works more slowly but finer.

I'm just spit balling here, but maybe the idea of using lather developed as honers (barbers, I guess) needed their hones to work fast, yet they wanted to create some form of buffer between edge and hone to avoid the harshness a 'raw', dry hone would provide. Water might slow down the process too much (even though I assume most barbers could do more strokes in ten seconds than many of us in a minute) and breaking the surface tension with lather might have been the ideal solution for fast, yet moderately refined results.