... it doesn't work!
I already tried it and yes, I can get a very nice black blade but no pamor visible. I also tried different concentrations but still the results are quite dissapointing. I also tried Nital and Ferric Chloride that I normally use for etching wootz blades, but with pathetic results. So, what works for etching wootz or blacking steel, apparently doesn't work for revealing the pamor... or at least I didn't know how to make it work.
PS: Selenium dioxide in diluted form works also fine for revealing the watering pattern of wootz.