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That is the real deal. All the synthetics were made to hone plane blades, chisels, and other tools. Some of them happen to work with razors. Some better than others.

Might be 45 minutes, might be a couple of hours ..... . :) Use the same procedure with the 4k as you do with any bevel set. Thumb nail test, shaving leg or arm hair, and especially examining the edge...