Specific material for dragon skin

I would like to remake this material which is on dragon image. I guess it’s a mix of glossy and diffuse with layer facing.
How to create these fine transitions to black gradient?
http://www.promisedland-artfestival.com/img/speaker-benmauro-img.jpg

Most of the look comes from the texturing and lighting, not the shader itself.

I guess it’s a mix of glossy and diffuse with layer facing

Yep, that’s basically it. Maybe mix diffuse with SSS prior to mixing with glossy, but beyond that it’s all in painting and lighting the model.