I have seen in several places that a specific gravity over 2.5 is considered True Hard which includes translucent and black. Hard Arkansas is between 2.30 and 2.45. From reading here and my experience all black and translucent Arkansas are not created equal. Do you have either a black or translucent that you use after a 12K stone and what is the sp gr? Please describe how you measured sp gr.

I measure volume by water displaced in a laboratory grade graduated cylinder then weigh the dry stone on a triple beam balance. I am not using distilled water and I did not correct for elevation. I have a 2x6 black with sp gr of 2.84 which I am experimenting with after my 12K Naniwa. Not sure if the edge is sharper but it definitely feels different. I also have a 2x4 black barber hone with sp gr of 3.23. I have not used this one enough to make any assessment.