I never really understood the nagura progression thing to be frank, except as a traditional way to hone and as a cheaper way to hone. The way I see it it is just a normal honing progression with slurry rather than stones.

In any event, if slurry dulling is created by a build-up of sludgy undiluted abrasive particulates and metal filings sitting in front of the edge and banging into it I don't see how that can be unique to a coticule. Many, dare I say all, stones can be slurried and many, dare I say all, slurries can be undiluted (just don't add water). But from what I've been reading here, it appears it only occurs with cotis?

James.