The goop on the blade is high temperature fireplace mortar (rated to 3000 degrees); for simplicity I just call it "clay". It's put on the blade before the hardening step. It slows the cooling of the spine to the point where the edge will harden fully and the spine will still be soft. You get the same effect as doing an edge quench, but you can do patterns (check out Don Fogg's stuff for some hamons that look like lightening!!)
After polishing the blade I etched it with acid. This acid mix was 1:1 archers etchant:white vinegar. Gives a brighter (and deeper) etch than the FeCl:water mix I normally use.
The edge on this knife should be around 60 Rc... the spine around 52 or so.