Here's a cool little guide on how to replicate commonly used zbrush brushes in mudbox: http://www.neilblevins.com/cg_education/zbrush_brushes_in_mudbox/zbrush_brushes_in_mudbox.htm
I would find a real picture (not a render) of the knife you are working on, or as close to it as possible, and try to replicate it. That is the best way to start tuning materials and mesh details. You have too many factors right now working against you to get an accurate shading model. I say temporarily ditch any sort of…
So in order to get gud at zbrush I decided to do some practice on some replication of older art. This is a recreation/interpretation of Crassus, one of the Triumphant of late Republic Rome.
For now the best way 2D artists can show their art is 'real' is to also show the process involved, ideally in video form, since AI can't replicate that (at least as far as I've seen). EDIT: Looks like I was wrong. :(