Smiles,

I'd recommend that you don't use a Thumb NAIL Test to attempt to verify the sharpness of your blade, you'll likely dull it by that means. The TNT test is used to help determine if all the mini or micro chips, chunks, and uneven sections of the edge have been smoothed out before going to finer stones in the honing process. What you may want to assay is the sharpness of the edge by means of the TPT, or Thumb PAD Test. With this you take the dampened, meaty, fingerprinted thumb "pad" and very lightly, ever so gently longitudinally and just barely, slightly latitudinally, drag it along the razor's edge to feel it oh so very easily slice into your epidermis. Once you've become accustomed to the feel of this hopefully less than minor surgery, you can use this test to help evaluate the quality of the edge before putting razor to face.

Comparing a TPT of a new double edge blade, used as a basis point, to your razor should give you a idea of how your straight razor should perform.

good luck, good shaving