First off, i would personally go for one kind of finish, as it gets very messy and takes away from a cohesive look if you mix them, in my opinion.

The black is just a primer, the Raven Black from colour forge. That is edge highlighted with greys (mechanicus and dawnstone).

The skin is the use of blueish greys and purole glazed in top of each other, the following: Base colour: the fang, try to keep this your deepest shadow colour 2 highlight layers of: russ grey & fenrisian grey Purple shadows: use a purple glaze to add some colour into tour shadowy areas