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The 20k is also cheaper, which is a good thing. :)

Neither is washing soda a detergent but still harmful. Norton's & Kings are a different animal & pretty bombproof. Ceramic stones are more susceptible.

What are the longterm effects of using soap on a ceramic stone ? Shapton advises against using any detergent on their stones.
Even washing soda can dissolve or soften some stones.

IME. Nope nothing at all. I bought one thinking I could speed up my honing by not using naturals.
Lately I use a synthetic bevel setter & 2 naturals & I'm done. Gotta love irony.