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Find a good true silk finish NOS vintage strop to go with the jnat, and you'll be pretty much set up forever - as long as your leather that goes along with it is hard, slick and shiny. I've cast off...

There are three 0.5 micron stones that I can think of, two shaptons (pro and glasstone) and the gokumyo. Each is a little different, I guess.

The closest thing that isn't expensive is the sigma...