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Thumbpad test is safe on sharp blades (safe for the blade. watch what you're doing with your thumb).
The pad is soft and sensitive. You've hurt your finger long before you've hurt the edge. Use a...

That really depends IMO.
A very sharp edge (hey, it came from Lynn) on a thumbnail would probably bite relatively deep. If you pull, the blade will then come loose and 'jump'.
The thumbnail test...

I hate to brake this to you, but this To verify this, I pulled the razor across my thumbnail, as when testing for a proper hone. I could feel it skip in a few spots. was when you destroyed your edge....